The problem with linux is getting started. I tried linux but was never able to get a miner working. (Tried with my 5870x2's, not the 6950's yet)
Edit: Alright, I tried the updated guide for 11.04, worked like a charm!
can you please point to the post-# you followed in this guide? http://forum.bitcoin.org/index.php?topic=7514.0;all
I tried #2, but actually something must have gone wrong as phoenix could not start (some opencl issues).
How exactly do you run your miners on Ubuntu? just start them in a terminal by hand, or did you write or found an easy to understand script for that purpose?