Having written a lot about YouTube recently, I stayed out of the fray yesterday when the video-sharing company unveiled new two advertising programs yesterday (with a little help from the notorious Paris Hilton). It got me thinking that while YouTube - and anything video, for that matter - is hot, what other Web 2.0 have as much buzz these days? More important, what are the hottest Web 2.0 businesses these days in terms of companies making revenue and profits? As Dead 2.0 made clear a few weeks ago, Web 2.0 is a lot like hot school. One day, you're red hot and you've got more friends than you'd ever imagine; the next all these people have moved on to the next new kid in town. If you've got suggestions and/or thoughts about whose hot and who's red hot, feel free to pass them along. Update: I guess Grouper is "hot" given it has been acquired by Sony Pictures for $65-million.