It just dawned on me that one of the reasons I started using Foursquare and Instagram is that their specialization means I can feel less narcissistic. This is distinct from the other advantages they have from being specialized (e.g., doing one thing really, really well), because it's mostly a psychological advantage.

They did this by giving me places where I'm expected to post my location and pictures. There's no technical reason why I couldn't have posted more pictures with Twitpic (the experience posting from Tweetie was actually pretty good), but I didn't because doing so somehow felt weird.

Put another way, my Twitter followers didn't sign up for a long stream of pictures or a bunch of checkins. Putting too many of either on Twitter feels spammy and presumptive. By starting new networks for these things, I can do them with impunity.