Just reporting that gnome-shell in latest Fedora 19 and the plugable UGA-2K-A usb2 works extremely well!
I have two 24" dell lcd’s and one 23", two directly connected to laptop docking station (thinkpad x230) and one of the 24" connected to the plugable.
As a test, I ran Team Fortress 2 (via native steam) full screen on one, a youtube vid on the other and an hd video in vlc on the third screen. Unbelievable! It just works!
Massive improvement over Fedora 18, really great!
Performance in gnome-shell is still not quite as good as 2d “fallback” mode is, but it’s now very usable!