Ha! Brilliant idea I just got from a Jezebel comments thread: to read a Kindle in the bathtub, seal it inside a cheapo ziplock-style bag. You still aren't going to want to, you know, hold it underwater and see what happens, but it should protect it from accidental splashing/edge-dipping, and you can still work the buttons/scrollwheel and read through the plastic. (Apparently the cheaper the better, because cheaper bags tend to be more transparent.)

I assume this tip would also work for ereaders like the Sony, the Nook, etc., but probably not for any ereader that relies on touchscreens.

(Total truth time: I have taken a Kindle into the bath, rarely, when I was reading something on it that I could not put down. But I always worry. This will reduce some worry. Presumably this would also be good for situations like the beach, where one might be concerned about getting grit in the device, although to be honest I've never worried about that kind of thing very much and my device is still in the land of the living.)

...hooray for solving extraordinarily first-world problems?