Personally I am more worried of a big company dominating more than one space. Say, I'm happy with PS3 to beat Xbox 'cause Sony is not a threat anywhere else, but Microsoft got the Windows/Office monopolies.

I am happy with Apple being strong in iPod/iPhone because they are weak in PCs. And I am happy with Google being strong in search, and Facebook and Twitter having the social network market.

If we got a Facebook killer from Twitter I'd love it. But from Google? I think they got enough fingers in enough pies for the time being. :)