XMonad 0.9 has been released. While I have been using the Darcs version for a while there looks to be a few features in 0.9 that I was not aware of. The changes since 0.8 page makes interesting reading and any XMonad users should check it out.
I'm still configuring Arch Linux x86_64 on my MacBook and everything seems to be working well except for the iSight. It appears to be possible to get it working using firmware extracted from a file in OSX. I never really used it and don't miss it enough to bother doing that. The brightness controls didn't initially work until I installed a daemon called pommed which handles the special Apple keys on the keyboard. Screen brightness is now easily adjustable.
I ordered 4Gb of RAM for it today so that should make it nice and snappy. It only came with 1 Gb with 144M of this being used by the integrated Intel graphics. 4Gb is probably overkill for my use but RAM is so cheap these days.
All in all it has been pretty easy installing Arch Linux on a Mac Book. I was expecting it to be more difficult. There is a pause during boot which I take is something to do with the machine looking for a GPT disk before it falls back to a MBR disk. It is not a huge hassle but if I find a way to prevent that without having to resort to using OSX as a second OS that would be cool.