It took me awhile but after searching various forums, I finally got my USBUIRT working in Ubuntu 10.04 with LIRC, and mapping the keys to XBMC works just fine.
HOWEVER...the range of reception of the USBUIRT is about oh, 3 inches. I am using as a remote the XBOX360 remote. Having such a short range really is a problem.
The machine I'm running it on is dual boot with Vista, and when I try the USBUIRT with Eventghost in Vista (all on the same hardware!), the range of the USBUIRT's reception with the same remote control is ten feet or more (limited by size of this room).
How do I fix the range issue? It's clearly not that my USBUIRT is damaged, or there's too much interference in the room or whatever--the same exact hardware works just fine under Vista+Eventghost. This is the last major hurdle for me in migrating from Windows to Ubuntu for my HTPC purposes.