Andres Nocioni had about as much offensive skill as Tyrus Thomas coming into the NBA.  Which made his 05/06 season amazing.  He jumped 6 points in PER, going from one of the worst players in the NBA to an above-average NBA player.  In one season he became one of the better stand-still jumpshooters in the NBA, going from .381 eFG% to a .494 eFG%.  However, both his 06/07 season and his age indicate that Noc has hit his ceiling.  His shooting improved slightly and before the injury so had his PER, but his skill level didn't.  He was just a little better at what he was already good at.  He once again was one of the league leaders in offensive fouls drawn even with the games missed.  Noc's turnover rate increased and his assist rate dropped.  

The Bulls were more effective with Noc off the court, but those numbers are misleading because Noc played almost half his minutes with Duhon starting.  There's no disputing that Noc is a flawed player.  He may shoot the ball too much, and he certainly turns it over too much.   He's a horrible perimeter defender, incapable of moving laterally or closing out  under control on jumpshooters.  But, he's a strong weakside defender with his ability to draw charges.  He's a very good rebounder for a 6'7" player, but never boxes out and needs space to jump.  He's a very good shooter (He had the highest TS% on the team until the injury affected his play, and is the best mid-range shooter on the team), but can be a blackhole on offense.  

All of that plus his ability to survive at PF at his size adds up to an effective player.  If you accept his PER before the Planter Fasciitis kicked in, then Noc ranked among the top 100 players in the NBA.  He ranked 79th with 0.696 PW% in 06/07 (68th PW%, 54th PW in 05/06).  I would also argue that Deng's drop in FG% after the first two months of the season was largely because of Noc's return to the bench. Noc opened up the lane for Deng.  (I'm not say that Noc should start because of that, I just noticed the correlation)  

There's a place for Noc on the Bulls as Deng's back up 8-12 min and another 10-20 min at PF.  I'd argue that he's clearly worth the mid-level exception, and probably another 1 million per season because Vladimir Radmanovic got 5 years-31 million last year to go snow boarding.  If Noc doesn't resign.  The Bulls need to replace him with two players.  A small forward that shoots the 3 consistently and a power forward that can shoot out to 18 feet.