Two year review
Then
There wasn't a day or an hour or a minute go by where I didn't think about my knees; I couldn't walk without pain; stairs were slow and painful up, slower and more painful down, hanging on for grim death to the bannister; everywhere I went I would be looking for somewhere to sit; all trips and outings had to be organised to minimise walking and standing.
At any time the knee could 'give way', or lock. I'd then need to visit my osteopath, who restored some mobility any number of times.
I could ride my bike, but only if I rode extremely low gears (100+ rpm) because I couldn't push hard; I had continuous saddle sores because of sitting awkwardly on the bike (I didn't know at the time what the cause was). I had shims fitted on the underside of my bike shoes to help straighten up; didn't work so well. I couldn't stand up on the pedals, I just had to pedal faster not harder.
I had to sell a fine Audi S8 motor car because the driver's footwell was slightly too narrow (caused by the diff for the AWD system) and my left knee hurt badly after about 45 minutes driving. Driving was always problematic, and I'd often have to stop to 'stretch my legs' because the hurt so much. I hated manual/stick shift cars.
Finally, my daughter said "On my wedding day I want to dance with my Dad; how's that going to work?"
Now
I go up stairs two at a time. Come down carrying things in both hands. Walk as far as I like - I'll often go to the bookshop, for instance, on foot, about a mile from my house. My knees are not a consideration in organising trips/holidays/whatever.
They never, ever give way.
My bike riding is limited only by my willingness to ride. My knees never hurt, I can ride such gears as I choose. I can stand on the pedals if I like. I don't get saddle sore any more because I now sit straight on the bike, where previously my knees forced me crooked. My legs are now the same length.
I can play table tennis properly, if not very well. 'Properly' means it ain't ping-pong, there's lots of movement and physicality to it.
Today I rode my bike 32 miles in 5 degrees C, strong winds. Knees no bother, rest of me... no comment. Yesterday played table tennis two hours.
I use a Ford Fiesta 1275cc for short journeys, where previously I would've always taken my Lexus 4-litre V8 just because it's auto. The wee Ford is tiny and great fun and uses about 1/4 of the petrol in urban driving -- driving never was fun before.
My range of movement is extension at -1 or a bit more, which is perfect (IMO anyway) and flexion around 135 or a bit more. I could get more I'm sure if I wanted to, but I keep forgetting.
That's key; my knees no longer dominate my life. Just how cool is that?
Added 6th Dec: I am 61, retired almost 3 years. I am now actively considering taking a long refresher course (actually an entry-level course, the business moves that fast) in progamming using modern methods, then taking on maybe a job, maybe a project, maybe freelance work. The course is 3 months from January 2014 and will involve walking 0.6 miles to the station, 40 minute tube ride maybe standing, and back obv. This would have been unthinkable and impossible prior to BTKR.