That is strange!
I used the USB install since the public beta, with no issues, the speed was also greatly reduced. I am really looking forward to the day when you buy something like Win7 it comes on a little USB stick rather than a stupid DVD.
Espesually things like server 2008, leave you playing the guess which servers have DVD drives rather than CD (honestly, you would naturally assume a dual xeon 5500 1u would have a DVD...)