Yay! Google released the Android 2.2 source today! I'll poke around at it over the next few days - maybe I'll have better luck getting it to compile! š
Update: I downgraded to gcc4.3 and Java SDK5, and Froyo is compiling fine. I'm still unable to boot the result though. š I'll try again tomorrow.
Update2: The kernel is booting, but /system isn't mounting, so 'sh' isn't available, and logcat can't run. Putting sh on the initrd changes the error - but it just quits directly after launching. Grrrr. Not sure why /system isn't mounting - the init.rc looks ok... I may try getting it to mount by it's device name instead of it's mtd name. I'm off to work - I'll poke at this some more when I get home.
Update 3: LiBe (in the comments below) managed to get 2.2 booting using Routehero's 2.0 boot.img. I just played around a little on my lunch break and was able to duplicate his results. Same issues as before - e.g. No sound, no radio, no wifi. The boot.img was still using the old 2.6.27 kernel. Replacing the 2.6.27 kernel with the 2.6.29 from V10T resulted in a non-booting boot.img, and as before logcat doesn't work so I can't even see why it's not booting. Grrrr. š
However - 2.2 did seem to run ok. Once I turned off Animations it even ran fairly fast. š