My favorite new feature (besides the massive improvements to Bridge) is
the alignment engine that makes handheld bracketed exposures an easy
deal. Stunning processing for out of alignment images. For High Dynamic
Range work, it's very cool.
You can see a comparison with CS2 at the following:
If you're interested, the "final" version is here:
This new alignment capability will also open doors for film shooters who
scan bracketed chromes or negs. Unlike digital captures that are pin
registered, there has been no easy way to scan different frames and
automatically have them registered. CS3 will change all that.
Oh, and finally we can hit the "P" key to turn Preview on-and-off in all
of the dialog boxes. Yeeha! And Curves is improved at last; there is
positively no reason to ever use Levels again.