@rgbeach
In another forum post, a user "studentofmusic" and I had a discussion when I discovered that I could edit a simple, software-instrument-only GB song in GarageBand-Mac's big brother, Logic Pro (Logic Express should do the same thing). (It made many complaints and created odd-looking artifacts, but I -could- get something I could edit.
He pointed out that if you choose a synth as your instrument and set it to "pitch" (pitch-bend), you get a super-pitchbend, which you can activate by touching a key and then waggling your finger right and left, that neither Logic Express / Pro nor GarageBand can produce exactly. That's only one element that makes me think that Apple has some major software work to do before you can really do the cross-editing that's still promised at
http://www.apple.com/ipad/from-the-app-store/garageband.html, in the Sharing item at the bottom of the page, just above Compatibility.
Note - no fix to the problem - Logic Pro can let you change the pitch-bend range of certain synth modules, but you really can't reproduce the rather stunning effect. Try it - I used "Soft Analog" from the "Synth Classics" instrument sub-section to get the effect. Try it, or send me an e-mail at nkellogg1@me.com and I can make a quick (and queasy-sounding) example.