For fantasy purposes, I like the Colts' running backs for the simple fact that Peyton will check the ball down to them a couple times a game. In 2010, Manning hit his running backs coming out of the backfield 55 times. Not a huge amount, but not insignificant either.
I'm not so much worried about how Indy's backs' will catch the ball, but much more importantly, how they're going to run it! Without a sufficient run game in Indy, what is going to stop defenses from bringing extra defenders down into the box, daring Manning to throw it. He'll do it, oh there's no question about that, but with a more productive run game, Manning could be primed for an even more spectacular statistical season.
I'm not sold on that happening though. At least not yet.
Indianapolis' run game has been sufficient enough for teams to now only stack eight in the box as opposed to nine. They're that bad. The last five seasons, they have averaged a finish of 25.6 in the NFL in rushing YPG, and have finished only as high as 18th (twice; 2006-2007).
Joseph Addai, though he'll only be turning 28, has beat up his body considerably through five years in the league. His between-the-tackle, physical running style finally caught up with him in 2010 when he missed eight games during the thick of the season with a shoulder injury (Much to the dismay of this fantasy owner).
The other running backs on the depth chart are adequate at best.
2009 first-round draft pick Donald Brown hasn't panned out yet. His 3.8 YPC doesn't warrant much attention, although his ability to catch the ball out of the backfield might keep him on the field on third downs if he can be trusted to pick up blitzers.
Michigan product Mike Hart has not been impressive either. Oh, and Javarris James who received so many of those Colt goal line touches last season, (five of his six touchdowns came inside the three-yard line, and the other was only six yards out?) He got picked up on a marijuana possession charge.
What you have is a handful of guys who have the talent, but not the necessary support in front of them to thrive.
You can't put blame on the running backs without putting it on the offensive-line unit. That is where the bigger problem lay for the Colts, the problem I feel could impact Manning's fantasy production the most.