Here are the new features from Calibre’s Changelog:
Update graphical toolkit to Qt 4.6 for better integration with Windows 7 and OS X Snow Leopard.
Device drivers: Support for device specific icons
Add menu options to delete specific formats/covers from the library
Metadata dialog: Auto-increment the series number when editing the series and validate the input ISBN based on the check digit
Add option to swap author first and last names when reading metadata from a file name
Replace underscores with spaces when reading metadata
Nook driver: Upload covers when sending to device. Also add Output Profile for the Nook
Clicking on row numbers in the book list will now open the book in the viewer
Driver for the Boox reader