I've been buying and collecting eBooks for many years now - while the Amazon Kindle reader is nice, on Windows Phone you can't read anything in your personal documents collection, and are limited to just Kindle titles.
Bookviser lets me work with my existing extensive collection, and thankfully has enough settings on the layout to provide the "left justified, black on white, small fonts and small margins" viewing experience that my brain expects from eBooks. I'll need to try a few books to get a real feel for the app, but I'm enjoying what I've found so far.
This is definitly one to check out. You can find Bookviser in the AAWP App Directory, or head over to their website (www.bookviser.com) to start uploading your own books and files.