i have 2 jetbook minis in my possession but i never really had an issue.
the second one i purchased off the ectaco site and received the 2gb sd card with 1000 books which is my savior every night when i get home.
i remember when the first jetBook came out it had SO many issues, but ectaco releases updates on a weekly basis and now the jetBook is superb in terms of format support and functionality.
im sure they'll do the same for the jetBook mini - and the best part is you get all the updates for free
i get the majority of my books from gutenberg, so i would recommend that site for well formatted books
the jb mini definitely has a lot of features and the design is super cool so like i said before i would def keep up to date with the firmware updates:
http://www.jetbookmini.com/update/