I've run Gentoo as my primary desktop OS for the last six years, and I really like it. Its extreme flexibility does have one major draw back though - it requires a significant amount of time to keep updated. I used to have the time to do that, now though, I have better things to do.
At work I run Kubuntu on my desktop, which I'm very happy with. Work don't pay me to maintain my own desktop, and I've spent very little time setting it up.
The big question now is how to replace Gentoo with Ubuntu without losing all my data. I'll probably buy a new harddrive, I could do with a new one anyway. That seems like the safest, if slightly expensive route.
Now all I need to find is a few hours to make the switch...