I'm seriously depressed by the number of social networking sites.
I'd disagree, but I know I'm in a small minority. I've never entirely understood the desire that people apparently have to bring their real-world identity onto the Net; I've always felt that going in the opposite direction (trivially changeable pseudonymous identities or just straight-up anonymity) would be more interesting[1]. Ignoring the oft-cited benefits for political dissidents, etc., I sometimes feel like we're losing the whole "on the Internet, no-one knows your a dog" thing, which I find a little saddening.
[1] Though "interesting" (my word) and "useful" (your word) are somewhat different criteria, I guess.