I'm 9 years out now on the first knee, 8 1/2 on the 2nd.
I doubt they'll last 20 years. I have about a 3.0 in pain for both, surely depends on weather.

The techniques are getting better all the time. If the choice is not being able to walk because of the pain, the surgery is a necessary option.
The recovery wasn't that bad w/ decent drugs for a couple weeks... still hate the stairs : )