There may be some higher mile bikes out there but the highest mile one I know of had about 340k on it - and was still running until some left turning hag took it out of commission. It belonged to Paul Glaves who is a Mr. Tech Guru on BMWs.
Old Smokey:
(http://web.bigbend.net/~glaves/kbike.jpg)
John Diaz did this a while back on his K75:
(http://i293.photobucket.com/albums/mm44/gator_motorrad/k75k.jpg)
DRxBMW who posts here has tons of miles on his too.
I bought a K75RT with 179k on it because I needed some fairing parts. I rode it home in one shot (1,231 miles) and it never skipped a beat. I've also purchased a couple of 100k bikes to use as parts bikes - both still running well but showing their age cosmetically.
Here's another benchmark on price (I'd sell it for more.)
http://seattle.craigslist.org/est/mcy/2898082644.html (http://seattle.craigslist.org/est/mcy/2898082644.html)