It seems insane that Bennett is drawing this much of a challenge in a primary so far out. I can't thing of a single issue where he isn't in lockstep with the citizens of this state. Maybe the flag-burning amendment, but that's pretty far off the radar right now. I can't imagine what he has done to piss off republicans.
Leavitt seems like a perennial nobody. It seems strange that Shurtleff would consider a challenge. Shurtleff has been a competent AG, and seems to be a pretty decent guy. An article in the Salt Lake Tribune today said that he is having discussions with his family about the race at this point. I'd probably take Shurtleff as a senator over Bennett, but it won't ever get that point. Bennett will be the republican nominee, and he will win the general election in 2010.
The issue that is causing problems is Immigration. Especially with Mexico collapsing and the Cartels recruiting Illegals within the US, this will be the issue in many primary campaigns and it could work even against an incumbent like Bennet.