We did it a few years ago and it was great fun - I've always wanted to go back, but am waiting for maybe next year when Zoe is 4! Be warned that it involves a lot of sugar!!!!!
I would highly recommend this to anyone, especially if you have kids or want a group bonding activity.
As to what it is, The Jazz Kitchen hosts a series of "Gingerbread House making parties". When we did it, it was $45 - not sure of current price - and we went in a group of 3 adults and 1 child (I was pregnant with #1 at the time). Every adult ticket includes the supplies for one standard size gingerbread house - pieces, covered board, frosting, and candies, and a souvenier Tshirt for the kids. I believe a drink was also included (food was available for purchase, too.
We arrived and lined up outside the restaurant. Then, they took us up to the top level of the restaurant and had tables set up. We gathered around as they gave instructions and then we were off on our own creative course. They had Santa there for the kids with Polaroid photos, and when you were done, they wrapped the whole thing in Saran Wrap, so you could take it home. I thought I had a photo of the one I did in my archive, but I can find it! If I do, I'll post it up.