I tried to post positive feedback and it wouldn't appear either.  I tried posting it three times.

I would keep trying (copy and paste it somewhere so you don't have to retype).  I did write a negative comment for a "Dr. B." in our area and listed something positive as well, which was that his office was conveniently located.  They didn't post that either, but I'm wondering if it was a server problem because it took me three days and about three tries each to get our pediatrician and endocrinologist's comments on there.  At least you got the neg. number ratings... it's so good you took the time.  Did they give you a note stating that they wouldn't post it?  I think they allow for neg. feedback because they allow the doctors to respond afterwards.