[ksloan2]

I suspect it has to do with the drop shadows of the windows, but shouldn't OS X have optimizations to prevent this?

It is especially visible in browsers when you watch videos from different sites. If a windows overlaps the video with just a few pixels, the performance is totally killed, but then restored once you remove the window.

I'm on a Macbook Pro 1.83, btw.

[TETENAL]

Video performance does not drop when windows overlap. Quartz Extreme does take care of that. You can verify this by dragging windows (transparent even) over a video playing in QuickTime Player.

What does happen is that Safari seems to update Flash less often in background windows (or maybe Flash does this voluntarily). I guess that is a performance optimization/compromise. So you see low framerates at Google video and Youtube in background windows. It doesn't matter whether the background video is overlapped or not.

[ksloan2]

Aha, I see. Thank you for the clarification.