The model is Edimax EW-7811UN 150Mbps Wireless Nano USB Adapter.
It doesn't work for more than a few minutes, but if I take it out and let it cool then insert it again, it works.
I was having the same problem with a Dell D1450U USB wireless card. The problem was almost certainly with software at some level and not hardware.
It may be faster to get back online - if you look under the menu for network settings
You may be better off posting in the Ubuntu Networking & Wireless forums where people can tell you what specific information could help diagnose the problem (ex. http://ubuntuforums.org/showthread.php?t=1818988).
Good luck!