We put one of these
http://www.perdueacoustics.com/drum_booth_kit.html in our "gymnatorium". We record each week just for reference to Pro Tools HD and edit/produce some of the special events for reproduction.
Pros: It was a massive improvement both for the live sound and the recordings. Pretty much 95% isolation. There is some low frequency bleed from the kick drum, but thats probably mostly sympathetic from the platform its on.
Cons: Pricey, and very time consuming to setup if you need to move it a lot. However, if you've got a minimum of 4 people to work on assembling it, it can be done very quickly. Its pretty clumsy to put up with 2 people, and impossible by yourself.