This is still very preliminary and could easily change as the PS games are played, but here's how I see our (deep) RB/FB situation.
Forte/Bush: The best 1-2 RB complimentary combo in the NFC. Don't change a thing.
Clutts: Yeah, I know some of it is the "cinderella story" aspect, but I like the guy and hope he sticks. He was a good blocker and decent ST guy for us last year. I hope he gets a shot and can convert a couple short-yardage 1sts and catch a couple balls in PS games to solidy his spot on the final roster. He's also our backup LS as of now and remember that Mannelly is less than a year out from ACL reconstruction surgery and at ~ age 35yo he may not be 100% so a backup LS may be more important than it usually is.
Booker: I don't know squat about him so I won't comment.
Bell: He's a less-talented version of Forte. Prob is never going to be a "feature" back anywhere but he can be a solid #2 or #3 man for several teams who don't have our depth. Main drawback/concern as far as that goes is that case of fumble-itis he picked up last year. Given the fact that he's not gonna crack the top 2 with the Bears and he's a FA next year, he's not likely to stick around anyway so I would shop him and take any reasonable offer. We are down 2 draft picks for 2013 anyway so a 5th or 6th doesn't seem unreasonable to me.
Allen: I really hope he continues to show in PS the potential we saw late last year. I'm pulling for him to stick as the #3 RB.
Unga: Based only on what I've read about him, he looks like an ideal PS candidate and I hope we can store him there for later use if needed.