iPad users: I've revised the overview at the head of
Calibre 0.7 + iPad: Start here to be current with the 0.7.3 release. Please post any iPad-related issues in that thread.
As soon as the next version of iBooks is released, I'll be working on adding PDF and iPhone support. I'm going to need the USB fingerprint of an iPhone 4 when they become available for any motivated early adopters.
G