Today I fired up conky and realized that only one of my cores was being used (I have an AMD X2 3800+). In Gentoo of course I compiled my own kernels, so I never had this kind of problem. I am still trying to get used to the idea of using a precompiled kernel in Ubuntu.
I searched the ubuntuforums for "smp" and came up with plenty of results. I needed to
apt-get install linux-686-smp. Simple enough. When you install a kernel in Ubuntu, it edits your grub.conf automatically and adds two entries: a normal entry and a "recovery mode" entry which I have yet to try. In any case it's nice not to have to do that manually.
I rebooted quickly and GDM failed to load due to the nvidia driver not loading. I tried to modprobe nvidia myself and got some really generic and unhelpful error message. I tried
sudo apt-cache search nvidia and got way more results than I'd hoped for, with no idea which was what I wanted. I tried nvidia-glx but I already had that installed. Same with nvidia-kernel-common.
So I resorted to
sudo apt-get install lynx and started googling. On the first page of results I got my answer: I needed to install linux-restricted-modules-2.6.17-10-generic.
But from the time of reboot to the time GDM was back up and running was STILL less time than it'd take me to compile a single kernel in Gentoo let alone manually copy the kernel to /boot, rename it nicely, fix up my grub.conf and then reboot and pray everything worked. What a world.