Some time in October 2008, I started a program of diet and exercise. Mostly the latter, but diet has played its role. My long-term goal was (and is) to avoid the fate of the elder Wagners; a big belly and a bad back by the time I'm 50. Much of my height is in my torso, which means I have an unusually long spine for someone of my height (190cm, or 6'3"). My back started to go out with uncomfortable frequency, and I had to do something about it.
My doctor gave me two choices for treatment: medication, and physiotherapy. It's always tempting to ask the doc for a pill that lets me keep doing what I'm doing, but not pay the consequences, but such a thing doesn't exist. So I chose the latter.
The doc sent me to an NHS physiotherapist, who examined me and concluded that I lack the musculature through my torso to adequately support my back. She prescribed a set of exercises that I could do at the gym and at home. Since I'd been paying for the gym for almost a year (but not using it), I decided to give it a shot.
I started working out 3 times a week, doing 40 minutes of cardio at peak heart rate (~170 bpm for me) plus some stretching and weight lifting through the chest. At home, I started a daily 20-minute warm-up routine in the morning, mostly sit-ups and push-ups. That first week I was miserable but determined. 5 push-ups was a struggle. Jamie has been an angel to support me, taking care of Pascale every morning while I do this.
About six months in, I decided to track my weight loss via
fitday.com. At that point I set a goal of 10 kilograms from when I started until my next birthday. I started at 95 kg, or 210 lbs. Fitday can work in metric but graphs only in imperial. The results:

Happy birthday to me! I turn 32 tomorrow, and I'm down to 84.5 kg. I can also now do 40 push-ups in one go, or 100 push-ups and 150 sit-ups in 8.5 minutes (thanks for that routine,
rezendi). I can run for 40 minutes without stopping, up and down hills and on dirt trails. I can pick up my daughter and carry her for a two-hour walk without my back going out.
My dad has the habit of taunting Jamie when we visit. "Do you like the belly? You'd better get used to it, because Tyler's going to have one just like it! Ha-ha-ha-ha!" You meant only a joke, Dad, but you lit a fire under my ass. I'm going to prove you wrong.
Lessons learned:
Your body is not supposed to support itself solely on your skeleton. You should rely on the static interplay of the muscles to move. When you aren't in shape, you spend a lot of time resting on your joints. Now I spend a lot of time resting on slightly tensed muscles. This is much better. I have very little joint pain now.
The physiotherapist was right. My back hasn't gone out in at least 10 months.
Score another one for NHS care. Time from seeing the doctor to seeing the physiotherapist: 3 days. Amount of money paid to NHS beyond what comes out of my paycheck: £0.