After (unsuccessfully) banging my head against the wall trying to sync my Ubuntu 10.04 laptop with the Nokia N900, I resorted to the only solution I knew would work.
I wiped out Ubuntu and installed Debian GNU/Linux Sid in its place. Apart from spending a night recovering from a dodgy dist-upgrade, the laptop now works, syncing perfectly with the N900.
Me, I think there is something wrong with Ubuntu 10.04.