Twitter status pages themselves are starting to get indexed by the search engines, and I would think many of these have been getting good Google PageRanks on their own. To illustrate, the twitter.com home page has a PageRank of 8/10, which is considerably high. Robert Scoble’s Twitter page has a pagerank of 5/10, while my own Twitter page has a PR of 4/10.
I think in this aspect, Twitter has an advantage over Jaiku, because Twitter statuses and user pages are set as subdirectories (i.e., twitter.com/username), while Jaiku uses subdomains (i.e., username.jaiku.com). SEO-wise, subfolders are treated as part of the original domain, while subdomains are treated as separate sites altogether. Therefore, whatever SEO benefits twitter.com is getting will trickle down to its subfolders, including user status pages and tweets.
I never thought of using such services to help promote myself and my blog, but it seems like it is already happening. Check out the full article on Blog Herald for more details. Very interesting issue that will have to be dealt with if we don’t want “cheaters” always outranking us.