The Aztech's, Team 157, used timing belts and pulleys on their 2005 robot. As far as I know, they didn't seem to have any problems with them. They used some fairly beefy belts, 1-1/4" to 1-1/2" wide, with a 3/8" or 1/2" pitch. They look to be fiber reinforced, so I can't comment on their strength. However, it was not a continuous loop, as the bot had two belts per side in a 4wd setup.
I'm waiting for a couple pics to be uploaded, stay tuned for links.
BEN