People have really been blogging since the 'net was invented. It's so very *not* Web2.0 that it's really cute when someone says it is. Blogging will still be around as long as there's a Net, long after the teens move on to the next big thing (think MySpace and GooTube joined together on steroids hooked into mobile phones, with video and voice chat and of course full gaming console accessibility).
As for the cream rising to the top - man, I wish. We've been wishing that for a long time, haven't we? And we're still having to fight the spammers daily, just as we have been for years. The cream doesn't rise to the top nearly as fast as the roach does that was hiding out in the bottom of the churn - and the cream goes bad long before he dies off.
The web has constantly been evolving, moving towards an extreme voyeurism where everyone is connected in their isolation. Blogs both feed that craving for interconnectedness and prolong the pain by keeping the user isolated; talking to his keyboard rather than a friend or loved one.
The adult blog that will really capture the movement will be one that leads two lives - one that users can check in on and get their fix while they're at work, because it's safe enough not to set off the porn filters; but one that also tells them where to go when they're home at night and can surf the dirty sites. How to actually accomplish that? I can think of a number of ways... it would be really fun to try.