I think friendfeed is eventually going to eat twitter's marketshare. It doesn't buy me all that much though, because I'm intentionally schizophrenic in the way I use the social web, trying (and, AFAICT, mostly succeeding) in segregating my personal, professional, and multiple web-social personae.
There's also the extreme danger of a) irritating the hell out of people who get five copies of everything you post, and b) feedback loops if you've used or are using multiple lifestream sites.
