I picked up a uno earlier toady and when I got it home I installed the IDE and drivers as per the website. it worked fine for all of about 15 minutes then I started getting com port in use errors. I disconnected / reconnected the Uno, but that didn't fix it. I rebooted the PC, but that didn't fix it either. By this point it wasnt even showing up on the com port list but as a unreconised USD device with no drivers installed (and it wont let me install drivers for it)
I have been able to get it to work for a minute or 2 at a time by uninstalling everything (conect the board, un install the drivers, disconnect, uninstall the IDE) then rebooting and reinstalling as per the website. This will work 20% of the time. When I get it to work it will some times let me do 1 upload (if at all) before it gives the comport in use error and starts the hassle all over again.
I am running Windows XP with SP3 installed. There is no firewall or AV running at this time.