Catalyst 11.6 warning
If you use AMD's Catalyst drivers on Windows, and you have more than one monitor, be aware that Catalyst 11.6 (the most recent version) enables AMD Overdrive (automatic overclocking) by default. On my computer at work (Radeon 3450 GPU), this caused intermittent (and really annoying) flickering lines on the second monitor. Disabling AMD Overdrive fixed the problem.
In short, WTF, AMD?