My new iBook’s trackpad was still acting up today, so I resorted to reading the instructions.
I was looking through the manual and it showed how to add memory or an Airport card by removing the keyboard. I didn’t need to do it, but hey, why not? Then I found I couldn’t get it back on, and realized the Airport card wasn’t seated properly. It was warping the keyboard when I tried to reinstall it. Since the keyboard hadn’t been warped before, I can only assume that the stress was being felt by the trackpad assembly, and since I’ve seen no further recurrence, I think I’ve fixed it.