I've heard that people who want to learn them should go for the USAW certification and avoid Crossfit. Even though Crossfit includes olympic lifts in their routine they focus way too much on volume and often don't teach the lifts correctly. Explosive lifts like the clean and jerk really should never require more than 4-6 reps or preferably fewer. I've seen crossfitter doing like 30 reps of the clean though.
I figure if you're doing 30 reps of anything then it's time to increase the damn weight.
Hit it on the head with that. I've seen lots of Crossfit people who have TERRIBLE form on their olympic lifts, for many it's more about getting the prescribed reps in the fastest time possible vs. having any semblance of decent technique.
USAW is the way to go for anyone who wants to learn the O-lifts properly, better to have someone who has been trained correctly in how to teach the lifts than someone who took a 2 hour seminar and got the stamp of approval to show someone how to do snatch properly!