Here is a short experience I had with a graphic card I once bought.
Buying a graphic card, is almost always come together with changing your PC. Your expectation from it is almost on par or even more then the CPU performance. Now here is the deal, changing a graphic card without re-installing the OS from scratch might cause some issues. Some of them are right after you fire your favorite application of game, and some of them crawl and appear just when you least expect them.
In my case, changing the graphic card cause X-Plane to not load at all, and when it loaded it had artifacts (this was XP issue but you don't always think of it on the first time). I remember receiving blank screen or crash before I could even move from the ramp.
The solution was to de-install the graphic driver and use some wiping applications, and then re-install the drivers from scratch. I admit that solved my problems.
BUT after two months, my PC started to crash it happened randomly after I loaded a 3D application, should be a heavy one, like X-Plane. This was very frustrating, since I wanted to enjoy the new card, as I should have. Trying to take it out and re-insert it again did nothing.
I then done the last thing I wanted to do: re-install all OSes that had this issue.
I re-installed my Windows and my Linux, my Mountain Lion does not seem to be affected but this is also a new OS and install.
Currently, I admit, there were no crash behaviors (knock on wood) and system seem to run better. I was even able to load X-Plane with HDR and Shadows set to high (before that x-plane crashed once shadow passed overlay option). I was even contacted by Ben Supnik regarding this issue, and I believe I can now send him my "workaround" to the issue which me and maybe another person had.
So, what is the conclusion from this post, When you buy a pricy piece of hardware, don't just stick it in and play, do a full restart of the system in order to be sure there is no crappy library that messes with your OS.
[I might also be wrong and my card might be broken, but so far so good - I'll update if there is any change for the worse]