With decades of Operating System experience under my belt, I have found some common issues with Operating Systems such as Windows, Ubuntu, and Mac.
The users knowledge of computers.
This is a leading cause of stress cancer, commonly known as "ugh, what an idiot."
A lot of times a user fails to read manuals given to them when they buy a horribly
expensive piece of crap computer, which is already five to ten years behind it's time. Yes, even the $6,000 computers.
If you don't know how to use ubuntu, or even read simple Tremulous engine errors, i'd suggest getting Windows or something. It's not your fault, it's the users' knowledge of the computer! Oh wait...