Speaking of knees, one of my other coworkers had a knee issue get aggravated in a Crossfit workout, one with squats at one of the stations. He got himself a brace after that and was told to take it easy for a couple weeks.

My dad remembers when they stopped doing squats in school gym classes (low squats, squat-thrusts, etc) because they were noticing people getting hurt. Most home exercise videos these days, if they even use squats, constantly tell the viewer to not drop farther than feels comfortable, or even stay above a 90-degree knee bend. If you modify burpees to use a wide, sumo-like stance, you can open up your knee angle, too.

I've got a tweaked left knee. When I did some medicine ball squats (squat down to tap your butt on a big medicine ball and go back up), they were a lot lower than I was accustomed to, and my knee was feeling it after just one round. I didn't want to push it very much after that.

OP, I'm sorry if I come across as such a Debbie Downer, but I honestly appreciate the enthusiasm surrounding Crossfit. I like the huge variety, and I've become more and more sold on the idea that isolating certain muscles via weight machines isn't truly productive. My concern is that the number of reps, the weights being used, and the speed aspect don't account for various fitness levels, and people start sacrificing form -- and possibly increase injury risk -- in order to complete the routine.