Shane Carwin has posted a blog saying that the UFC 108 bout with Brock Lesnar is off and that Lesnar has Mono. Carwin also says in his blog entry that the UFC has told him he is the number one contender and that he just has to wait for Lesnar to be healthy.
The next most likely date for the fight between Carwin and Lesnar is UFC 109 on Febuary 6th, which is the annual UFC card the night before the Super Bowl. Though with Mono it may be even longer than that.
Also the cancellation of this fight gives credibility to the rumors that Cain Velasquez will face Big Nog at UFC 108. that has been reported by Tatamae but Velasquez's camp is apparently not confirming the report.