If an ad blinks in the background, does anyone see it?

Or more specifically, is the thing eating cpu cycles on my computer? Say you visit a site and it’s got several of those wonderful attention grabbing blinking ads from hell. ESPN has them for example, as does Bluewsnews and the IMDB on occasion. They’re all over the place, really. The definitely eat cpu cycles on my machines, especially on the Mac if they’re flash based, you can actually see the slowdown of the browser’s ability to scroll when they’re on screen. My question then – if the browser is minimized or occluded by some other app’s screen or the finder or whatever, and the screen with the ad is not visible, is it still eating cpu cycles? Intuition would say not, but some testing on my laptop was inconclusive. Anyone know? Lacking a working commenting system you’ll have to IM me if you know the answer, or email me to one of the addresses on my contact page.