Carticel / ACI - But how good is good?

I'm 35, and have had 3 knee surgeries to repair and/or investigate a 4cm cartilage defect in my left lateral femoral condyle. Initially the Dr. did a microfracture procedure and I recovered well. I have a nice-looking fibrocartilage coating over the defect, and it pleased the Dr. very much to see it. After this first procedure, I can waterski and bike, but I can't run. Going up and down stairs can "remind me" that the injury is still there. I can't really lift weights for too many days before a soreness sets in. I can snowboard for one day but then it will be too sore to walk. I've been leading this kind of life for about 2 years now. In doing all this and trying to live a normal life, i'm probably wearing out the good cartilage in the rest of my knee, working itself slowly towards arthritis. I've read in discussion forums that many patients who have done the ACI procedure are happy and recovering, however none of the reports really sound like people are fully back to normal, or even close. This hasn't really increased my confidence in going forward with an ACI procedure. Additionally, many doctors, even experienced in ACI, often throw in the "are you sure you're ready to do this?" comment. Aargh! So a big question for me, and probably many others, is there anyone out there actually doing sports more or less fully recovered without too much worry? Of course we all tend to be much more careful after surgery, but a true rehab means you feel strong and can get over most of your worries, and do what you want to do. Has anyone really got to this level of rehab after the ACI procedure? If so, we'd love to hear from you!