I've recently purchased Progression for the ipad. It's a tab writing app that has a lot of very cool features that help to make the guitar sounds and playback more realistic: bending, sliding, hammering, etc. I love the fact that wherever I may be with my ipad, I can get my ideas down fast. I can compose on the fly and when I get back to my guitar, i can print out the tabs and see how well i can play what I've composed. It's not only an excellent tool for composing but also for practicing my chops.
I've been improving my guitar skills with Progression for the Ipad. It's very useful for composing and writing tabs. Now if only I can play as well well as I compose on my Ipad! ...but as they say, practice makes perfect.
Yes, during one of my songs, I reach up from my guitar and place a b3 like solo on garageband...it actually sounds real. Good thing I have small fingers. The Ipad and GarageBand has changed everthing for me. My $2500 midi file workstation sits with dust covers on it..idle.
Just did back up tracks for Classical Gas. I now play like Mason Williams with an orchestra behind me...too cool. (The orchestra made that song.)
Have you checked out the iPad/iPhone TouchOSC app? I think it's about $6 or $7 (USA).
Funny enough I've been using the Reason Rebirth app ($5) for generating beats and very simple arpeggios and i love it... haha, so oldskool but works very well once you get used to the scrolling and zooming headache :P