What an excellent software! Beyond comparison with the alternatives. As good as Stanza for iPhone, but much better than both Stanza and eReader (or anything for that matter) for desktop!
Its user interface is, unlike the competitors', very Macintosh-worthy. Voluminous has an integrated literature database (no need to seek it online: just type it in Voluminous and press "enter" - it will immediately fetch the book for you).
This is how I expect an eBook reader for the Mac to look and feel. The developer must consider programming for iPhone as well. My compliments!