When the 250 only date the 250When we popularized "the 250" as a nickname for San Francisco's Internet cool-kids crowd, we didn't realize how literal the incest was. Take the flirtation between Flickr's engineering chief, Cal Henderson, and Ariel Waldman, the community manager of Pownce, an online file-sharing service. Pownce was cofounded by Leah Culver, Henderson's ex-girlfriend, who has also dated around the scene. Henderson and Waldman traveled to Hawaii together, and have made jokes — on Twitter and Flickr, of course — about Henderson wishing Waldman shared his last name and calling her his "fake wife." It's all so darling, veering on disturbing.When the 250 only date the 250Social networks — the kind Henderson and Waldman work on when they're not using them to flirt — are supposed to expand our worlds. Yet these websites' real effect is to shrink them. Who'd want to start anything with anyone who's not already registered on all the same websites you use? The training time to explain the twee etiquette of Web 2.0 is a barrier to entry more fearsome than any Google or Microsoft might dream up. It can only lead to San Francisco's insider scene becoming literally inbred. (Photo by bees))