A co-ed bachelor/bachelorette party can be a LOT of fun. I didn't do it for my wedding, but I've been involved with the planning of several bachelorette parties, one of which was co-ed.
I think the best solution for this type of event is to spend part of the night with just the girls and then meet up later with the guys. That way you get to have some festive girl-only time, but still have the thrill of co-ed partying. Since I've been a bride, maid of honor and bridesmaid multiple times, I decided to put together a website with everything I learned. For some fun co-ed bachelor/bachelorette party ideas, check out my thoughts here:
Co-ed bachelorette party .