I've run Knoppix and Puppy as livecds, but never tried installing. Puppy had a really great installation guide, as I remember; how to partition and everything. It might be fun to install and see how fast it is from the harddisc, which should at least decrease boot-time, even if running it isn't faster, since I have enough RAM (2GB).

(ETA: I think my main problem with getting OpenSolaris to play nice was using the ext4 filesystem - OpenSolaris obviously couldn't detect Ubuntu - and I'm wondering if I'll have the same trouble with Puppy. Guess I'll find out.)

I think you may want to look for a distro that will help you solve a problem that Ubuntu's not helping with or that does something besides run your desktop like Ubuntu
That makes good sense!