I recently upgraded from the original Aperture (Ver. 1.2) to this new version (Ver. 2.1), and I am very happy with it.
Image editing enhancements aside (there's many a tutorial and explanation on the Apple website), the major criticism I found with Aperture 1 was that it was a massive memory hog, mostly due to the program being designed for Power-PC architecture. This meant that when editing photos or loading up the program on my Intel-Macbook, the software was very 'heavy' and laggy at times.
This version is now configured to work with Intel-chipsets in the current Macintosh lineup and as such operates far more smoothly and requires much less memory to run. It has also been 'polished' to be consistent with the aesthetic changes in OSX Leopard.
Aperture is far superior to Apple's iPhoto, and also can export files to be edited in external programs, such as Photoshop. For organising a large photo library and all the non-destructive image-editing that goes with it (files remain in tact, only the changes are saved and applied when viewing and exporting the images, saving on crucial hard-drive space) this program is essential, if not amazingly beneficial to professionals and amateur photographers alike. A long overdue upgrade to an amazingly useful program.