Dude, if Pennington can stay healthy all year (which I don't see as a problem unless he gets into some freak preseason accident), I think he'll finish the season as a top-10 QB for sure. Honestly, I think that as long as Santana Moss continues to improve himself and McCareins proves to be the No. 2 threat that the Jets need to keep defenses honest, then Pennington will be a top 5 QB IMO. He has amazing accuracy and doesn't back down from pressure.
The big thing that I think people worry about in the rankings you're seeing is the running game. Obviously Curtis Martin's time is about up and they need to start transitioning the running game over to LaMont (who I think is in a contract year, so they need to move this year). If that transition falters for some reason, then I could see Pennington strugggling a little. But just a little.
Just don't make too much noise about him -- I'm hoping to snag him in a late round at a value spot!!