I just finished the Wilton Method Course 1: Decorating Basics as well as course 2 at one of my local craft stores. I'm taking the classes with my mom, and it is quite fun. If you want to see if they offer classes near you, do a search on their site.
Now, what did I think? Our instructor was quite helpful and very nice. She made sure that any questions we had were answered. I didn't really know the first thing about how to decorate when I started, and I feel much more comfortable now. We have just started class 3 and it is so much fun!
If there is anything I would complain about, it's the class prices. I don't think they're high (especially with the coupons!), but the sheer amount of STUFF you have to buy is a little daunting. You have to get your class kit, your instruction book, and some other things like a cake turntable if you don't already have one. You can do without the turntable probably, but it would make things much more difficult.
Plan on spending at least what you paid for your class on materials. So with a $45 class fee, it's about an additional $45. Not bad for 4 weeks of classes at 2 hours a pop, but if you're not expecting and budgeting for it, it can be a little much.
Watch for buy one get one deals on classes. If you want to take the classes with a friend then it works out perfectly for the first class if you're not quite sure that you are interested in taking all 4 classes.
My first cake. I got lazy with the border.
My final cake from the second class: