Okay, here's my impression after 1 evening with it and sleeping on it.
I spent $10 last night. 2 singles and an album (a White Witch I didn't even know existed). The singles were 99 cents, the album was $7.99 with 10 tracks. Everything worked perfectly. One of the singles was a song I already had on my iPod to use as a reference for comparison. It sounds at least as good as the 192kbs MP3 already on the iPod using my cheap home headphones. I'll know better today when I get to work where I keep the serious headphones.
The more I think about it, the thing I believe is really revolutionary is that Apple convinced the credit card companies to accept many thousands of sub-$1 payments. I don't think this has been done before and could open the door for all kinds of micro-payment systems.
Here are some more screenshots if anyone wants them.
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