Apple has also added mock-pressure support into the app using the iPad's accelerometers. GarageBand uses these sensors to determine the amount of force with which each finger taps, much like a piano's mechanical keyboard does in real life, producing softer or louder sounds in response.
Wow, this is kind of blowing my mind. You can see it in action 39 seconds into this video at the GarageBand site, and at 49m51s in the video of the iPad 2 event. (I never watch the iLife/GarageBand demos at the Mac OS X events, and readily dismiss articles discussing these sorts of things because they rarely interest me. It seems I did the same thing when watching the iPad 2 event last week and reading about it in the interim, and missed this little gem of a feature.)