A quick update: I got the memory upgrade from 512MB to 2GB for my powerbook, and it has helped performance hugely. Meanwhile, Maya's MacBook had become similarly unusable in much the same ways as mine--a lot of quality beachball time--despite her using it for nothing other than web browsing and word processing the vast majority of the time. So I got her the same upgrade. Fortunately the memory was pretty cheap. But this is a bit ridiculous. I'm not sure who to blame: Apple, Firefox, or people who make websites. Should a MacBook out of the box be insufficient for web browsing?