Last year they scaled back Percy in the offense to keep him on the field. He didn't like that so they centralized him and now he's hurt. He appears to make it to most games, but he has a hard time staying on the field. It's a significant concern for a guy with his style of play.
I doubt they trade Percy for anything but a 1st. They can go Carson Palmer on Percy, and that is the last thing Harvin and his agent would ever want going into the prime of his career.
I'd have a tough time stomaching the trade of a first round pick for anything less than another first round pick. Percy hasn't exactly been a bust either. If they think the problem is Percy and it's worth not having him, then just play it year to year and frachize the guy if they decide they want to work something out.
Personally, I think Percy wouldn't be nearly as difficult if the QB situation was a bit better. AP is the show on this team, but the QB needs to be good enough to get the ball out. I shutter to think what AP could have done had someone like Matt Stafford been manning the helm. I think getting Alex Smith this offseason would be very wise, especially since his value is low enough that they won't likely have to give up their first rounder.
I doubt anyone would be able to keep from laughing if you told them Percy for a first rounder straight up. He only has one cheap year left and that is the value of the first round. Get an impact player that keeps you under the cap. I do think you could gain a very valuable pick if you were willing to move back in the first round and add a second rounder. The other scenario is to use Percy to move up in the first round but I doubt you would be able to move up past slot 7-8 even with Percy and the Vikes first rounder.
I'll keep my Paul Allen thoughts to myself, suffice to say his level of annoyance makes me genuinely wish harm upon him.