In this essay on sociability Simmel constructed around this concept deals with a wide range of issues based on various conceptions of social interactions. The central subject taken into consideration is contention that communication as a particular form of social interaction is not obligatory to be rationally planned, calculated in terms of potential costs and benefits, or have strategic intentions. Simmel's proposition that there are forms and cases of conversations realized just for the sake of conversation is in fact a pure forerunner of the forthcoming in several decades theory of communication with R. Jacobson's classification of communicative act's functions  . Thus, I think, that sociability's function is a sort of mixture of two marked out by Jacobson: fatic, or contact-establishing function which key sense is in building and confirming the very fact of existing communication and check out if the channel of connection (medium) is working; and referential (communicative) which stands upon contexts and transmit information about things, objects and events.
I would agree with Simmel on relevance of playfulness element in what he calls sociability and this of course leads us to Gofman's drama approach and concept of play frames in everyday interactions. But was is really disputable to my mind is his statement on equality of those who "play" that way: there are many cases of unsymmetrical relations (e.g., hierarchical ones in formal organizations) that do not exclude that playful component of conversation and even flirting with is ambivalence of intentions and polysemantical actions. Moreover, the latter often serves to reproduce and reestablish not only gender roles and behavioral patterns but micro social structure.
Speaking about "the stranger" Simmel maintains that a certain social type can indicate an individual not for his own decision to be of that type, but as a label of a relationship to a particular social group.
As far as I can judge this essay can be considered as Simmel's impact into development of marginality conception and a precursor of Samners conception of contrasting "we-group" and "they-group". Indeed strangers ambivalent position of a so to say "necessary outsider" is about interplay between opposite positions of an accepted member and a total exile. It seems to me that already mentioned Gofman was to some extent guided by Simmel which reveals itself in a way in his idea of stigmatized identity.
Talking about fashion Simmel continues the line of analyzing social phenomena through interplay between two poles. Such approach seems to me the most relevant in this case, because I consider fashion one of the most ambiguous social phenomenons which core idea is based on balancing between stable and transient. If go further, we can find out a paradox: it usually happens that the more an individual tries to stand out of the crowd, the more alike a certain crowd he becomes, the more ordinary his image gets. May be the thing is in finding the right group to oppose to and to differ from? Question of the difference between being "fashionable" and being "stylish" is appropriate here as well. It is definitely a fruitful topic for an independent essay.
Though framing of individual representations in a massive visual space seem to me more adequate approach now, but Simmel's traditional idea of class-related and cyclic origin of fashion is well-grounded and still up-to-date.
Not less fresh perspective is performed in "The Metropolos and Mental Life". Coherently with Simmel Louis Wirth in his "Urbanism as a way of life" scrutinizes effects that individuals face in the process of rural-urban transformation. After all, Wirth tries to stand more non-judgemental while Simmel roughly criticizes urban way of living, using terms "unthinkable mental condition", "disruption" and others. Although, I would argue what Simmel saw as negative can provide us with mixed interpretations and there can be not less but much more emotionally rich stimuli in the life of a city-dweller rather than that of rural community.
Considering meaninglessness of urban life and blasé attitude of the city dwellers, I guess, Simmel was rather taking into account only those relatively short periods of dramatic changes in individuals' self construals when they resettled from a countryside to a city - for those who live in the cities for a long time, no distinctive cultural-mental shocks should appear, as far as I see it.
It is also interesting to mention that Simmel's critical approach to modernization resembles that of neomarxists from Frankfurt School towards culture, consumption, loss of individuality and growth of calculating rationality in the period of transition from modernity to post-modernity.
Returning in this context to already mentioned Wirth, I would like to underline that he saw modernization and urbanization as at least intercorrelated processes. Grounding his arguments on understanding sociology's instrument - ideal types - he examines a distinction between rural and urban forms of social communities, postulating that "The central problem of the sociologist of the city is to discover the forms of social action and organization that typically emerge in â€¦"  (what he calls a city).
Giving a thorough description of the role of the city in contemporary civilization, he analyzed which features of settlements of then modern times can indicate the city. Here I will briefly foreground what is not a city and how we can follow to its adequate understanding. Cities are not only about big numbers of population as the urbanization touches and changes almost every single aspect of individuals' lives. City is not only about density of population and physical size of the settlement - these are not enough to form a relevant definition because the borders and differences between cities and rural settlements can not be minimized to what is of physical volume. They are quite vague, uncertain and lie in the field of lifestyle varieties. "A sociological definition must obviously be inclusive enough to comprise whatever essential characteristics these different types of cities have in common as social entities, but it obviously cannot be so detailed as to take account of all the variationsâ€¦"  . Thus, urbanism in general is not only about cities but their dramatic influence on modes of individuals' lives.
Wirth contends that up to that date there was much literature on urbanism but there often occurred mixture of close concepts urbanism, capitalism and industrialsm, it was not enough compendent with a few exclusions. That is why he formulated relatively specified research problem and a basic definition of the city that dealt not only with that simply calculable indicators but also with permanence of the studied settlement and social heterogeneousity of its dwellers.
I doubt that the latter point can be put as an argument or even a strict reason for settling together - heterogeneousity itself is too much an ambiguous stimulus for setting off rural way of life. I agree that much more differentiated than of rural communities content of the cities means their quality differentiation which leads to physical segregation and fragmentation of social interactions. However, rational motives of lessening resource deprivation predefined by the place of living seem to me more relevant. And moreover there is a positive effect of urbanization in these terms: amplifying the weak connections' power (Granowetter) and sociability (Simmel).
Wirth offers a certain operationalization of the main concepts used in his work "from three interrelated perspectives:
as a physical structure comprising a population base, a technology, and an ecological order;
as a system of social organization involving a characteristic social structure, a series of social institutions, and a typical pattern of social relationships;
and as a set of attitudes and ideas, and a constellation of personalities engaging in typical forms of collective behavior and subject to characteristic mechanisms of social control." 
These may be debatable but they perform a new to date vision of analyzing urbanistic lifestyle.
In conclusion I would consider what is really important and interesting for me in terms of allusions to contemporary social phenomema. It is that process of urbanization seem to be very much alike the process of virtualization: "In a community composed of a larger number of individuals than can know one another intimately and can be assembled in one spot, it becomes necessary to communicate through indirect mediumsâ€¦" 
"Being reduced to a stage of virtual impotence as an individual, the urbanite is bound to exert himself by joining with others of similar interest into organized groups to obtain his ends. This results in the enormous multiplication of voluntary organizations directed toward as great a variety of objectives as there are human needs and interests." <â€¦> "Since for most group purposes it is impossible in the city to appeal individually to the large number of discrete and differentiated individuals, and since it is only through the organizations to which men belong that their interests and resources can be enlisted for a collective cause, it may be inferred that social control in the city should typically proceed through formally organized groups." 
Change here "voluntary organizations" and "formally organized groups" to Internet communities (of all kinds) and you will get a certain retrospective replica of what happens today during social interactions more and more swap to the network media.