Well I wouldn't classify him as a star, but he does ride a Triumph America. His name is Oteil Burbridge. Yeah, I know what you're thinking...who dat? He's a bass player that has been with the Allman Brothers Band on the 2003 "Hittin the Note" album. He's also recorded with Phish keyboardist Page McConnell, and recorded and toured with Gov't Mule.
So how did I find this out? Well I was just searching on Google for Triumph motorcycles in the news, and came across
this article. If you read down a ways to about the 5 paragraph or so, you come across this; "(When Preview caught up with Burbridge, he was cruising around Birmingham on his Triumph America motorcycle)".
Anyway, kind of cool to see a musician of his caliber riding the same bike we do....even if it is a slower America.

I also did a search using his name and came across his official website. There's a forum there so I posted an invite to this site. Who knows, maybe he'll show up here sometime.