On Ubuntu, the recommended epub viewer is Firefox plugin
epubreader
or fbreader (sudo apt-get install fbreader).
They both have book category to manage books which have been read.
The firefox plugin sometimes displays texts in epub files a mess, while fbreader always displays in the right way.
Calibre and Okular are both heavy-weight app, large and slow when startup.
Calibre has stand-alone ebook viewer "ebook-viewer", start it in terminal:
$ ebook-viewer <filename>
I also tried view mobi file with okular on Linux Mint 14 Xfce. But its KDE mobi plugin "kdegraphics-mobipocket" doesn't work.
Updated in 2016.2.5: Okular supports j/k to move page. Toggle any UI components in [main menu -> Settings].