I've been using it for the past eight months or so and I am incredibly happy with the results that I have seen. For those that don't know, StudioPress released its Genesis Framework with the hope of making it easier for the designers to make custom themes without having to touch the intricate coding. This resulted in a very detailed, secure and search engine optimized theme that could then have any look you wanted.
Since launching my own company, I've been using the framework and the child themes to build sites for my clients. It allows me to stay away from the overly intense coding, but I can still make a really nice looking site for small businesses. I've had a lot of favorite themes before, but these take the cake. It's designed by the same guy who created the Revolution themes, so we can imagine that he knows what he's doing.