Yes, it's amazing what IK Multimedia and others are coming out with for the iOS devices, isn't it?
I've got Peavey's AmpKitLink for the guitar --> iphone connection and have been experimenting with both the Amplitube and AmpKit apps. I'm a pretty novice user in this regard so far though - had only been using the free versions till now although your post is whetting my appetite again to expand my virtual gear with some upgrades now.
I think eventually I'd like to get an iPad for the extra screen real estate it offers to make things a little less cramped, plus for some of the unique offerings for it such as the iO Dock
The world of iOS music gear is developing so fast that's it's a bit overwhelming for me to try to keep up with it all. So thanks for starting this thread!