After seeing it in stock through their inventory locator, I drove by Circuit City yesterday to try and get myself an xbox 360. Since the store is about 20 minutes from my home, there was a pretty big chance they'd be gone by the time I got there, and they were indeed nowhere to be found in the showroom by that time. Then I noticed an employee carrying two to a counter, so I followed him, asked if they had more in stock (the ones he carried were spoken for), and was finally able to get me one.
When I asked the guy why they hadn't put them on the floor, he responded "we can't - there would be fights", suggesting this had actually occurred before. Then again, in an attempt to sell me their $70 extended warranty, he also told me half of them were returned to the store because of defects, so he wasn't exactly that trustworthy I guess.
For people still looking for one: Best Buy also has an inventory locator (though it's a bit buggy), or you could subscribe to xbox360tracker's RSS feed to be notified of availability at dozens of online stores.