I had the same problem as already described in:
http://support.plugable.com/plugable/…
The adapter was not recognized after rebooting the computer.
My Solution:
I tried a USB2VGA device from a different manufacturer before, which did not work but installed several Drivers…
After uninstalling these Drivers, the Plugable adapter works perfectly!
Maybe that helps somebody
(Plugable USB-VGA-165, Win 7, Geforce 9500 GT, USB 2.0)