Hm. I tried that but it didn't help. You're right: all-day events work fine when I change the week's starting day to Monday, for example. But when I switch back to Sunday, it goes back to the messed up stuff. Does it on multiple calendars, too, and even with different users. So I think it's something to do with my iCal application. Weirdly, it also affects my roommate's iBook, so I wonder if this is some kind of a virus thing? (I seriously doubt it, but I'm looking at all possibilities.)