Ability to merge clips with synced audio, more trimming options and few more new features. If you go to www.adobe.com, it will tell you all the new features. Overall, I found its performance better than CS5. In fact, I can't remember the last time I opened the CS5 version.
I just had to upgrade to keep things consistent on a project with a producer using CS5.5... that said, the warp stabilizer in After Effects 5.5 is freaking amazing.
Yeah, I saw an example where some guy gave his kid (maybe 3years old?) a camera to hold aimed out the window of a moving car.
Of course the shot was shaky, and you can use AE's stabilization tools in CS5, but in this example you can't easily fit a point to stabilize because *everything* in the shot is moving!
So using the new warp stabilizer preset, it actually manages to find its own set of points (that must vary every few frames or something), and even helped reduce skew and jello. I must admit, I don't own 5.5 (still on 5 myself), but that alone was pretty compelling.
Actually, looking at upgrade pricing, etc, I'm wondering if the whole suite is worthwhile, or just After Effects 5.5 for the Warp Stabilizer. That is pretty compelling of a feature, but the other stuff doesn't seem like its worth the cost of an incremental upgrade. Unless I'm missing something else that is mind-blowing?