It's worth noting that I have about a thousand devices in the field drawing from 1.25A to 2A @12V through the Arduino Vin pin (to a shield), and none of them have burned out any traces or melted any pins in the Arduino =)
The biggest concern I had originally, was the trace size from the dc plug to the Vin pin, which seems fairly small, and AFAIK the Arduino boards use 1oz pours. (My shield uses 20 mil traces for the biggest consuming paths, and 2oz pours.) However, this has not proven out to be an issue. However, I still have some serious concerns in the long run, considering a lot of the female headers I see out there are rated @ 2A through each contact. I don't know the specific P/N of the headers used in the Arduino, but I'd bet money on them being around the same.
!c