I've been looking at Web 2.0 sites more following downloading the excellent Flock browser which is one of the best that I've seen for handling all my social media and RSS needs. Though I've been noticing some simialrities between Web 1.0 and 2.0 - in that there is a lot of money probably being put in by venture capitalists into these sites I didn't realise how many sites there where out there until I say the directory of web 2.0 sites that some one has compiled at go2web20.
I don't think even allowing for the incredible growth of this market, that all these sites are going to be taken over by Google/Microsoft et al - so some of these are going to either fold or consolidate over the next year or so especially as the credit crunch bites in the global economy. I've tended to stick with social media that I think is likely to make it through either because of it's connections with large players - or it's ability to stand on its own financially (in my unsophisticated opinion.
Just something for you to think about when using social media for something work related. Being cuatious I have both browser and social bookmarking for all my bookmarks just in case one of the SM sites folds.