If I knew do you think I’d tell you :p
I don’t think anyone but the companies buying / investing in these startups, or the startups themselves really know who’re going to make it.
You really don’t hear a lot about new technologies until they’re ready to go and in everyone’s faces. But that’s very broad.
Rather, I think Tumblr.com is getting there, for a few reasons. Mainly that it’s the annoying part of Myspace (the bulletins) plus followers, aka friends, but harder to obtain, along with twitter integration they’re golden. As soon as they figure out how to monetize that hot shit :p