He's better than Grease-pit.
With that said it's obvious there's better, but the fact that he can run around makes him somewhat of a challenge when your trying to keep an eye on guys like Sharpe, Lilile or Smith.
I think all in all the Broncos are an amazingly athletic team in every position, and combined with Plummers 4 years in the NFL, your bound to put something together.
Plummer is never going to be a stand out QB, without the Broncos he'd be doing exactly what he did in AZ right now.
PS: I think his major downfall is going to be those overthrows I keep seeing from him, at some points it's like watching Quincy Carter playing last year.