I never took one, but I did go to help with teaching one. We had a guy that put it together and it was a disaster. If a tying class is done right I can see where it could be a great thing. In the one and only class I have ever been a part of though, It was a waste of time except for where I personally helped this blind guy learn. He is the same blind guy I helped in the rod building class. Because he was blind, he did not really follow the rest of the class, which was primaritly a "Hey, look how great I am" brag session by the guy who put the class together. He sucked, the class sucked and pretty much everyone but the blind guy left with a foul taste over the whole thing.
By the way, the blind guy did an awsome job on the 9' 6 wt. he built, and he ties flies pretty well also. He does wood work. He's amazing.