If I'd known I could do this, I wouldn't be so cautious about app purchases!
The most interesting thing was that they don't do anything to take the app back. I received a refund, but still have the app on my phone. In fact I think it's even been updated since without a problem.
Here's a snippet from the email from Apple support.
"I have reversed the charge for the accidental purchase you reported. Please note that the iTunes Store Terms of Sale state that all sales are final, so this is a one-time exception."
> (I’m not sure how the IRS W-9 cut is handled; that’s about 28% in the U.S. It would suck if the IRS keeps that cut until tax time.)