I mentioned that when I tried Ubuntu 6.10 in Parallels, it didn’t seem to support the maximum resolution offered by my MacBook’s screen. Instead of getting a resolution of 1280×800, I was getting 1024×768, which meant that everything was fixed in a square in the middle of the screen.
A number of people suggested ways of fixing this (sadly all of them involved editing scary-looking configuration files or running scary-looking configuration utilities as root in the terminal) but nothing I tried seemed to work – I was still stuck with 1024×768.
And then I installed the latest build of Parallels – beta 3, instead of beta 2 – and suddenly the resolution is perfect. It turns out the problem was a bug in Parallels, not a problem with Ubuntu. So I can enjoy Linux in full widescreen glory.