My gaming group tried 4E and it split the group down the middle. Several players, mostly people who preferred non-D&D games and only played D&D to appease everyone else, really liked 4E and declared they would only play 4E from that point on if we wanted to play D&D (not coincidentally, they were also big WoW fans).

The rest of us didn't like 4E, though we spent about 3 months playing it and trying to make it work. We compromised by playing some other games for a while, but D&D had always been our default game and every time we went back to it things would bog down into edition wars. The other players weren't even willing to try Pathfinder. So in the end the group splintered apart.

Ironically, I don't think 4E is a particularly bad rules-set and take no pleasure from its failure. In fact, it would make an excellent rules-set for a MALAZAN RPG (where even common grunts can take on gods and survive). It just isn't really the same game as D&D, and throws too much out in an attempt to be relevant and modern.