I've done a bit of BJJ. I used to play a lot of rugby, to a reasonable standard, and obviously train functional strength at the gym, but doing something like Judo or BJJ it's amazing how even though I'm way above average strength it doesn't always equate to dominating your opponent. That's what I enjoyed about BJJ it's about grappling and using skill rather than all out strength. Don't get me wrong having strength helps ultimately, but it is how you apply the strength that's more important.
I loved watching the Judo and TKD at the Olympics - so much stamina and control - great stuff. Learning for the sport and the discipline is the way to do it, doing it for anything else is plain stupid.
I did some door work for a while and the amount of people that did "moves" to try and put you off or scare you is quite pathetic - it's a shame the wrong people learn it for the wrong reasons.
Anyway, great to see people doing Martial Arts and exercise/sport - it's good! And if you can help defend yourself in a situation where you can't run away so much the better.