Just remember for those who are gym shy, there are Zumba DVD's. I bought it way long ago before the huge craze hit the last few years.
I have taken classes and though teachers do go through Zumba certified training, each class can be very different. A lot of teachers are jumping on the bandwagon, so some classes can be a disappointment. You can tell the difference between someone who truly loves doing the class and someone out to make money. I guess just like teaching in the real world too.