At least with Cam Newton - just as with Tim Tebow before him - you can convert him to tight end once you realize he'll never succeed as an NFL QB.
Cam needs to thank Michael Vick for the season he had last year.
Tebow has played, what, a quarter of a season. It's a bit early to write the guy off. You never know when these guys will catch fire. Case in point, look at Bucs QB Josh Freeman.
In 2009, he went through his growing pains just like Tebow. But, in 2010 he really stepped it up and almost took the Bucs to the playoffs.