Suma (ArmA Lead Programmer) im BI-Forum:
"We would like to notify you we have identified a bug in the ATI drivers, which can cause gradual performance degradation while playing ArmA. The bug is confirmed by the ATI team and they are working on a fix. The bug can be seen both in Catalyst 7.1 and 7.2, we did not test with older versions yet.
While uploading geometry data to the card, driver sometimes opens a process handle without closing it later, resulting in a leaked handle. If you are an advanced user, you can verify if you are affected by the issue by checking the handle count in the Task manager while running ArmA in a window. If you see handle count raising gradually,
As a temporary workaround, you can set both the Texture Detail and the Object Detail to Low Very Low to reduce the effect of the leak, and restart the game after playing a few missions.
You could also choose to install somewhat older Catalyst 6.7 drivers available at ATI Web Site, which do not have this problem. Note: installing older driver may degrade performance or cause visual artifacts in in other games, especially in those which were released recently.
We are sorry for the inconvenience and we will notify you once we know more about the fix availability from ATI.
It seems the Catalyst 6.7 does not have this problem, while 6.9 seems to have it. Not sure about 6.8 yet."