My T40 (2373-8CM) started to drop USB2 devices back to USB1 and telling me I should use the available USB2 ports. (of course there are only 2 ports and they are USB2). I tried all the driver and bios updates, no joy there.
Finally rang IBM service and they tried to say it was drivers etc, and denied any issues with hardware. After a little crankiness on my part they said they would pick it up for service.
To my delight they replicated the problem once they had my T40. Fix was a new main board, changed under warranty. I now have my T40 back good as new!
My advice is push the issue for service, as there seems to be a USB issue with some T40's that only a new main board can fix.
Hope this is of some help.