It sounds pretty good (i'm using irig input) and there are quite a lot of add-ons/options (a little expensive tho- $6 for extra mp head/cab combo's)
(Does it sound as good/better than amplitube's? I'll let you be the judge- but i like it and you can never have too many varieties!
There's a free version without much in it but probably worth checking first
Watch your ears as some settings get mighty feedback thru headphones
(at least using the irig -there is a feedback supress button..
n.b-luckily it doesn't seem to feedback thru speakers in the same way)
just letting you know..
(bring on the iphone hate