I haven't had a knee replacement yet but have been told I'll need one, some day. And to put it off as long as possible.
Three friends, family member, and mum of a friend have had it done.
My mate's mum now in her 80's had her's replaced some years ago. Her surgeon said something along the lines of "I'll do them both at the same time, because if I do them one at a time, you won't come back for the second operation." She by all accounts is getting on famously.
A friend had one knee replaced in 2004, about the same time a second friend had a hip replacement. The hip replacement friend booked herself into a rehab facility post op, whereas the knee friend chose to do it herself. The hip replacement was more successful than the knee replacement.
My brother in law had one knee replaced 10 or so years ago. He's had so much trouble with semi-permanent infections, restricted movement, and chronic pain, that he won't have the second done, even though it gives him a fair bit of curry.