Yeah, Kasparov lost the world championships to Kramnik two years ago. It was more of a testament to Kramniks preparation than anything though, since he came in with openings that Kasparov was totally unprepared for. Since then Kasparov has regrouped and has once again proven that he is the best player in the world, winning many tournaments including ones Kramnik participated in, and he'll retake the throne again when he likely meets against Kramnik later on this year in the World Championships.
You're right though that he isn't the world champion, my bad :) I do think he is the best player in the world, Kramnik looked horrible in the tournament just held in Wijk Aan Zee.
I do disagree though that Deep Blue was unprejudiced, the thing was created more or less as an Anti-Kasparov machine. It was "trained" to play moves and go into positions that were very much against his style of play. I think many other weaker players would have faired better against it, although who really knows since it got dismantled. Most other computer programs aren't prejudiced though.
I think it'll be a long time before they make an unbeatable computer. The problem is that there are just too many positions that really need to be understood 20-30 moves deep, something far beyond what a computer can see at this point. Kasparov showed time and time again that a computer just doesn't understand the idea of a "plan", as it constantly made moves that made no sense when considering previous moves. Unfortunately he just wasn't able to exploit this weakness this time :)