Ive read that twitter is a waste of time, as of yet i have no plan to use it, soon something else will come out and everyone will jump on that and twitter will be so 2009. Doubt google will do that tbh.
Youtube is likely to stay around for a while, while I don't think anyone would actually use twitter 2 years from now. (coming from a person with a Xk followers, using twitter daily)
I've checked that few months back and Google can use Twitter for current revenue but also future revenues (Including more users to use G services, Adsense on status pages) And so on.
Twitter is very popular internationally, and the popularity is growing in the United States. I admit that it's a pretty strange forum for exchanging ideas. There is a lot of junk that gets passed around in Tweets. But it's still evolving, and I think it will continue to grow in the U.S. in the future.