My wife and I bought the Proform XP Trainer 580 in Feb 09. We used it for the past 10 months without issues..Except that it contained to left cupholders.
My son was running on it on Nov 30, 09 and the treadmill stopped abruptly causing him to fall and injure himself. I originally thought he had stepped off the side, but after some investigation I found that the drive motor had separated from the motor mount causing the drive belt to come off which resulted in the walking belt stopping abruptly...He didn't. He ran into the cross bar and fell backwards on the belt injuring his back.
It appears the tension on the drive belt was so great that it caused one of the two motor mount bolts to shear off. I did some research and couldn't find where this has happened before...It may have been a defective bolt, but in any case I felt this warranted a warning to other consumers.