I made the switch to 3.0 and immediately hated it. It had many redeeming qualities, but ruined my existing campaign. The house rules were so built into the 2e system and the deities and faiths were impossible to recreate in 3.0 (My biggest complaint with the system).
When I switched, I first tried to re-build my world, it didn't work and I quit DMing. The CR system didn't scale for large parties (I have never played with less than 7 people since picking up D&D again (after a break of 4 years) in 1994.) The stress of rules and balance led to burn out and I wasn't having any fun anymore. I decided to play, and frankly wasn't all that impressed then either.
Seeing my failures and noting the failures of the DM I was playing with at the time, I approached him about building a shared world, where we both ran it and controlled different aspects, allowing us to create multiple NPCs for encounters without one person having to play all of them. For the last three years, its worked, not always well, but its worked. So I wasn't so much of a hater as an apathetic participant.
4e is a chance to move the campaign towards a larger and more expansive vision. If I can create the fluff because the crunch is simple and self-explanatory, then I'm ready for 4e now. If it just bogs me down with aids and accessories, it will be time to re-evaluate whether D&D is right for me.