One thing I don't like about either the PRS-500 or the PRS-505 Reader is the small size of the next page/previous page buttons, and the fact that they are nearly flush with the case. Kindle's user interface is something of a mess, but one thing they got right was the large page-turn duttons on both edges.
There's no way to retrofit large buttons to the Sony readers, but the existing buttons can at least be made "feelable," so that you can locate them by touch. Just mix up a small amount of epoxy cement, then use a toothpick to apply very small amounts to the key buttons... until you've built up a tiny, glossy bump on each button.
It's a small thing, but I find that being able to easily locate the buttons by feel makes turning the page just a little easier, as a bonus... and because of the epoxy bumps, you don't have to push as hard. And it looks as good as if the manufacturer had designed it that way! :-)
Andy Baird
http://www.andybaird.com/travels/