I upgraded to Ubuntu 9.10 on my MacBook (hardware version 4,1), and I'm lovin' it! It's a major improvement, especially since they fixed a lot of the issues that were plaguing me and my MacBook.
I like the new theme and background.
I always swap my control key and my capslock key. Now, hitting control finally makes the capslock key light turn on.
Getting my wireless card to work was easy.
Getting an external monitor to work was much easier than last time. I didn't even have to edit xorg.conf!
Sound works by default, and it sounds better. There was a bug in older versions where the mid-range speaker wasn't turned on.
The touchpad is much better by default, and there's even a user interface to improve it further. I like to turn off touch to tap and switch from edge scrolling to two finger scrolling. The speed and acceleration are perfect by default. Setting up the trackpad so that it wasn't insane was my biggest challenge under Ubuntu 9.04.
Power management continues to be a breeze.
Supposedly all the other things like the iSight camera and microphone are also working well, although I haven't gotten a chance to try them.
I also like the fact that the applets are toned down a bit. It fits in perfectly with my recent sentiments on "calm computing".
Anyway, this is the happiest I've been with Linux in a long time :)
By the way, here's the web page for running Ubuntu 9.10 (Karmic Koala) on a MacBook version 4,1.