I like the ebook to at least contain the cover image and any other images, maps, etc that were in the original paper book. This rarely happens, but MS reader format ebooks _do_ tend to include them, which is handy
Other features like you mentioned are interesting, and might make the reading experience better for some, but others might find them distracting. You also need to consider what's being read. I don't think I'd like to see animations in a novel, for instance, but an etext book or manual would really benefit from extra features like this, and might really open up ebook versions as worthy alternatives to the paper versions.