I could program an Arduino with a pair of tweezers, son.
...
Seriously, I have no idea. I suppose Apple's too cool for USB ports, but maybe Wifi? That ups the cost of your Arduino setup, it's true, but still - there has to be something you can do to communicate between your iPad and your Arduino that doesn't involve a general-purpose machine in between.
There's now a blessed serial cable with a dock connector, and some form of an arduino programming environment on the iPad. The only drawback is that the cable is more expensive than the arduino.
But as an aside, can you program an Arduino if all you have is an iPad? Or would you have to go buy a general-purpose PC for somewhat more than $30?