iBooks 1.2 has been released [iTunes link] for the iPad, iPhone 4 and iPod touch, and it brings with it support for Apple's AirPrint wireless printing technology among other things. The new ereader app now supports Collections, by default set to splitting up ebooks and PDFs, but which can be used to group titles however you prefer.
As for AirPrint, unsurprisingly that won't allow you to print ebooks themselves, only PDF files you've loaded or annotations you've made to titles. The usual sharing icon has been extended in both cases to include "Print", and then the normal AirPrint dialog in iOS 4.2 is available. Finally, there's support for new, fully-illustrated books as well as automatic hyphenation to split words across sentences as appropriate. iBooks is a free download in the App Store.