I defentinetly plan on buying garageband on day one for my iPad.
Not getting the iPad 2, even though it does seem very cool.
I don't think it'll be a huge lag fest, it does only record 8 tracks (lame).
I can see mobile garageband being a useful tool for on the fly inspiration recordings, I don't think too many people are gonna be able to have very complex songs with only 8 tracks. I make electronically, I have no idea how rock would work. I bet the iPad would be decently useful for bands just starting out wanting to record something quick.
-I don't think it'll lag on the first gen ipad.
-I think 8 tracks is limiting this app extremely, but with so little ram, I can't imagine they'd give us much more anyways.