milehighmilitiaperformance in ubuntu seems inconsistent at best. every once in a while my fps would drop to ~40 which is terrible. This will probably get better as the drivers become more and more commonly supported, but at this point i dont think linux is a viable option for competitive gaming.
I only have that issue when I very first go into a server, I'm guessing its because its still "loading" parts of the game, because my install is on a "normal" slow hard drive.
Outside of that, I've not had this issue what so ever.