Well, since this 4-year old post, I have had a knee replaced and lost more than 50 lbs. Unlike bkbjones, I don't keep my heart in my knee, so they didn't have to deal with that.
Only missed one season and haven't had any issue.
The other knee which was due to be replaced last March is still there. Apparently, the support of the new knee and lost of weight gave the knee a break and is actually in better shape than before. Go figure.
Its only a matter of time before it will need to be replaced and I don't care. If it happens, it happens and I'm okay with that.