Culpepper CAN be an elite QB, but I dont see the tools there yet for him to be one in Miami. He is a pretty good pocket passer, and a very good runner.
The thing he doesn't do well is move around in the pocket, and thats why he failed last year in Minnesota. The way Marino used to move in the pocket, and sidestep the rush- Culpepper hasn't shown that. There is a very real chance that he plays horribly, and gets hurt again. They need better blocking.
On the other hand, don't be shocked if Joey Harrington steps in and plays at a VERY high level for them, and even gets them to the playoffs. His skill set is very different that Culpeppers, or what was asked of him in Detroit, where he never fit in. I think he could end up starting next season