I downloaded GarageBand for my ipad2 and was blown away. It's not a full-blown pro tool but it is a preview of how touch technology will play out. The smart instruments sound incredibly good, the B3 with drawbars and Leslie is tremendous, the velocity sensitivity is ingenious, the acoustic bass is a blast to play, and the depth of guitar sounds, patterns, techniques is amazing for an app that cost $4.99. The 8-track recorder/mixer and audio recording makes jotting down song ideas on the road a snap.
Omni TR is already blazing ahead in the tablet space and together with what we see in Garagband it appears touch screen tablets are going to become very important performance tools.