The Cubs selected Mark Pawelek with their #1 pick (#20 overall) in the 2005 Rule 4 (June) draft. He was the 4th HS pitcher selected in the '05 draft, but he almost certainly would have gone higher if it wasn't for the fact that he had Scott Boras as an "advisor" (unofficial agent) and that he had signed a Natioal Letter of Intent to attend Arizona State. But the Cubs were able to sign him, and he reported initially to the AZL Cubs at Fitch Park.
I saw Mark Pawelek in his first pro season at AZL Mesa (2005), and I can tell you he was as good as advertised (94 MPH fastball, plus-curve, plus-slider, and plus-change). Then he went to the AZ Instructional League post-2005, and the Cubs coaches apparently started tinkering with his pitch selections, delivery, arm slot, release point, etc (probably with the intention of trying to prevent an arm injury), and he gradually just lost confidence.
The Pawelek Family is very unusual, in that the dad fancies himself a pitching coach, and is very involved in Mark's career. His dad pitches for a top senior team, and he really knows his stuff. But he's kind of like Mike Marshall, in that he has a somewhat different approach than do most minor league pitching coaches.
Mark and his older brother Dennis (who was drafted by the White Sox, but chose to play college football instead) had a special work-out regimen back home in Utah, where their dad had them throw every day, and where Mark and Dennis were taught a particular philosophy of pitch selection.
Unfortunately, the Cubs have only one way for everybody, and Mark was forced to conform to the Cubs Way (especially when it came to side sessions and pitch selection), and apparently it messed him up.
The Cubs claimed Pawelek came to Minor League Camp in 2006 "out of shape," but he wasn't overweight or anything, he was just "messed up" mentally and his mechanics were out of whack, to where his velocity was down into the mid-80's and he couldn't throw any of his "hard" pitches (fastball and slider) for strikes. And he kept hitting batters. How much of that stemmed from his work in the AZ Instructional League after the 2005 season, I don't know, but his confidence was clearly adversely affected and he couldn't get back to where he was at AZL Cubs in 2005.
There is nothing wrong with Mark Pawelek's arm. His problems have all been related to messed-up mechanics that caused his velocity to drop into the mid-80's and his command to go haywire (where he started hitting batters with regularity), and then (with the drop in velocity and loss of command) a confidence issue ensued.
I talked to a scout from another organization last year, and he said his club is just waiting for the Cubs to give up on Pawelek so that his club can get him and "pick up the pieces." (The Cubs minor league pitching coaches are not held in real high esteem by some of the other organizations, BTW).
From what I can see, Pawelek at least appears to be getting his confidence and enthusiasm back, and he's once again relying on his innate talent and just cutting the ball loose and then whatever happens, happens. While he might continue to struggle some with command (and what 21-year old hard-throwing left-hander doesn't?), if he's got his confidence and enthusiasm back, that's half the battle.