I've been using the Barnes and Noble app on my Blackberry. It's not too bad if I've got 10-15 minutes to kill and nothing but my phone to play with. It's better than BrickBreaker. It also helps that I can easily read 9pt font without straining so I don't have to continuously be "flipping" pages.
Surely it's no different to just browsing the web on your phone? Sure the text is small, but if you can read it and don't mind doing so, why not have a couple of books on there to pass the time when need be?