As for the sound card - I agree, the DAC in the iPad is probably similar to the other iDevices in the past.. Pretty good for consumer standards, but poor by pro standards - not to mention multiple outs, ins, etc. Where the iPad stands to gain the most is as a remote controller for a larger rig running on a laptop - via Bluetooth or Wifi. Heck the audio jack could be used for modulated data and have it interpreted by the host machine as a control input, a la Serato et al. Ever since the $2k Lemur people have been hungering for this - it will happen sooner or later!
Consider that the passion of musicians to produce their music has led to eons of refinement in interface and design, A material technology which the hi tech world with its planned obsolescence paradigm does not often appreciate.
All innovation is welcome and exciting, few things in the world of a musician brings more joy then a discovery of a new sound, or a new technique he can learn.
but you know? that guitar interface? it just works.
... Of course the touch screen is exciting for musicians... check out Amit Pitaru/Zach Gage bring Sonic Wire Sculptor. its fun
Now, I can turn a 10" screen into any imaginable control surface, including using all 10 fingers to move multiple objects at the same time. It's heaven. The iPad does what you would have had to spend $thousands for previously in the recording/mixing world.
Snobbish bullshit like this is a bigger threat to creativity than anything the iPad does or doesn't do.
More specifically, I'm saying I think doing so is a part of what keeps people out of making music--the idea that you have to be "serious" about it by spending a lot of money on recording gear or it somehow doesn't count. Far too often it's just the opposite: people just blow money on the gear because buying things is fun and they tell themselves they need it to make better music. And hey, maybe people will end up buying some iPads for that stupid reason, too. The point is that the cost of the gear and "seriousness" are not so directly related. I don't mean there is never a relation, only that you can't really draw this kind of generalized meritocratic conclusion about the art and artist from something so independent of their actual merit as the tools they use.
You may think it's snobbish, but that's reality in the pro music world.
Again, I wasn't saying that desiring the best sound quality is snobbish. What I think is snobbish is assuming that only professional musicians are serious, or that someone who involves an iPad in their musical process is somehow inherently less serious than one who doesn't.
EDIT: Here he is playing the iPhone in the middle of his keyboard solo, live: http://www.youtube.com/watch?v=ONGpprZBkrs