You know, I think Reddit is actually the best positioned Twitter alternative. You can use your real name, or anonymous account. You go there to follow particular subreddits, but there no reason why I shouldn't also be able to follow people and see their non-topic (ie, not part of any subreddit) microblogs interweaved with posts from subreddits. They deal with spam and trolls reasonably well.
They have all the pieces, they just have to put them together tastefully.