My buddy Caroline wrote this terrific feature on the supposed social phenomenon of Urban Tribes, an article I had a little hand in. The idea is that due to various factors, including: (1) postponement of marriage due to economic and educational trends; (2) new telecommunications technology which results in easier organizing of groups; (3) disposable income and more cultural distractions; (4) shifting attitudes about institutions, the "tribe" (a group of close-knit friends) has become the central social unit for increasing numbers of late twentysomething/early thirtysomething urban types. The point isn't that this is somehow a new thing, but that "tribes" have expanded in far greater numbers in recent years.
Maybe "urban tribe" is just a fashionable tag for a old hat, maybe it's a real thing. But when folks are coming up with such lame terms as "quirkyalones", it tells you that the race to coin the "post-millennial yuppie" moniker has reached absurd levels.