I'd had it, that was the straw that broke the camel's back. Even though I had a paid version of AVG (and about a year and a half left on it!), I uninstalled it. (And the uninstaller failed the first time through.) Version 7.5 was pretty good, but 8.0 is just unusable.
Since I'm not running 2000 Server anymore, I decided to go back to Eset NOD32, and I'm amazed at the difference. When I had AVG installed, the CPU meter in the Vista Sidebar kept spiking to 50-75% all the time. I'd assumed that was just Vista being a processor hog, even though I've got a fairly beefy quad-core CPU. But now that I'm running NOD32, the CPU meter is running about 1-3% most of the time. I'm not sure whether that means AVG is that bad or NOD32 is that good, or both.
I'm rather annoyed that I paid good money for AVG and it's unusable.