One thing you can be sure of is that very soon there will be a deluge of applications for the Apple iPad - and quick off the mark with a sound recording application is Sonoma Wire Works, with their application StudioTrack
This is what they say about it:-
StudioTrack is a powerful songwriting tool for musicians who want to capture musical ideas and record songs on the iPad. Every channel includes a reverb send and a configurable effects rack. Effect options include a delay, EQ, and a compressor.
The master channel has a Reverb Return knob as well as a parametric
EQ and a stereo master compressor-limiter. StudioTrack multitrack
recorder for iPad, developed by Sonoma Wire Works and Retronyms, is
now available on iTunes for $39.99.
StudioTrack Features, Images, Video & Support:
On the fly arrangement of chords and melody