I've done this at least twice now
sudo apt-get install ruby-compass
Real easy, right? Wrong. Ruby blogs go ballistic over how awesome rvm, how flawed the debian method for managing ruby is. Rvm is awesome because since you can run different versions of ruby during development; whatever.
Hey, Ms. Fancypants, I just want to compile sass files.
So, next time I install compass on ubuntu, these steps (which uses rvm) worked great.