Among the exercise physiology and biomechanics people I know, Crossfit has a horrible reputation. The problem with it, as it has been described to me, is the fact that it places a greater priority on the number of reps completed than the form maintained during those reps.
A prime example of this is the prevalence of kipping pullups in Crossfit programs, where participants are encouraged to kick their legs (to 'kip') so as to lessen the upper-body strain. The problem with this is that it actually places greater strain on one's joints, which isn't really a good thing.
I've also seen a fair number of Crossfit videos where people use improper form in benching (bouncing the bar), squatting (knees too far forward), deadlifting (rounded backs), and the like.
I hope that helps!