I've been using iRig for a few months now. I think, for what it is, it's a great practice tool - especially with the speed trainer functionality - and I use it for late night backing track jamming over headphones.
I loaded everything and have been so busy that I haven't really used it yet. I have a pandora px4 too which I fall back too as I know how to use it pretty good...
I hope to spend some more time with the iRig...seems cool though. Too back there isn't drum or backing tracks preloaded like the Pandora.