I want to start out by stating that I hate the Bears. However it's hard to ignore what Devin Hester has accomplished on special teams. I remember Coach Smith talking about getting Hester in on offense towards the end of last season. I just didn't realize that it would take 8 months to design a "go-route" for arguably their best "offensive" player.
Hester is the only guy in the league with speed comparable to Steve Smith. Obviously there's no comparison between the two in terms of being a complete wide-out, but I would think the coaches would spend every minute of practice working with him. Smith is the most explosive WR in the NFL, and you can't coach speed. Even an 80% version of him in route running would be a big time weapon. There's a lot that goes into the position that doesn't show up on go-routes though, like running routes and blocking.
I dont know if Hester has been on the field enough as an offensive player to qualify as 'not very good' or a decoy. (7 plays, thrown to 5 times, 2 catches, 1 TD) But Hester is a sick talent and the Bears have to figure out a way to use him even if he's just a decoy that's being used to stretch the field.