web: it's one social network, not 1000 sites
All these sites are converging to the same set of features: picture uploads, a blog, commenting or replying to other posts, find like-minded people based on interests, and tagging. Even though they all seem different, you can tell they're the same thing because they all output RSS feeds.
Not only do they keep reinventing the wheel, they make me maintain a set of wheels in 100+ towns across the 'net. The only value is if I want to remain a different person in each town — the sex-crazed female elf, the abusive technogeek, the sober businessman, and only I know they're all me. But if I want to integrate my selves, it's a complete pain. Every time I write something elsewhere, I have to consider whether to repeat it here or link to it (which pushes my readers themselves into joining yetanothersite), or let it slide.
The Web itself is THE social network. You put something on it, I link to it. It's unnatural and unconvincing to restrict social networks within it to a particular site. It's entirely possible and straightforward for my link to indicate the type of relationship: she's my friend, this is a reply, this is a review, etc. and for us both to keep track of the link.
Unfortunately, there's an impetus to own a set of eyeballs, to get and keep users on MySpace or some arcane bulletin board so you can present lots of ads and eventually sell out for millions.
I hope the costs of identity management — dealing with fake users, abusers, lost passwords, etc. — will push sites to trust third party identity services. I should be able to hand "Joe's cellphone php BulletinBoard" my identity and authentication token and an e-mail contact, and not have to sign up for their site. They can trust that identity more than their own membership form because I paid real money to get it. (Wayyyy back in Netscape 3.0 Gold time, I paid $10 for a Verisign class 3 identity and public key, but I haven't used it in 8 years.)
Even with federated identity and single sign-on, that still leaves my thoughts spread out all over. Sites make me to come to them to post, but that's short-sighted. If I'm writing a feverish reply correcting someone's William Gibson bibliography, I'm not going to click on any ads. Instead, sites should pull in responses from all over the net, so readers spend more time on the site. I post on my site about them, they show that content on their site.
One other value to all these social sites is that they're free and in a features war. I pay to have my own place on the Web (skierpage.com), and although monkeybrains are fine people for Web hosting, this dump only has a storage locker and an electrical outlet. There is no picture upload, forum, Web 2.0 animated social tagging, etc. at skierpage.com. But for privacy, control, and copyright issues I don't want to lose my primitive house and join the condo association at Myspace. All software features should trend to $0 cost so eventually I'll have them here.