I finished up the first round of my side project: PeerGym http://www.peergym.com let's you search for quality gyms in your area by membership price and amenities - the kinds of things services like Google Maps and Yelp don't do. Most people do a particular kind of workout (running, weights), and need special equipment (treadmill, barbells), and you can't always guarantee you'll know what you're getting just by the na…
I think it's a nice project, well executed and sorta scratches an itch. I think if you actually want to try to get some usage, you're going to really have to put your business/growth hat on and really try and understand why people would use it, how they're going to find it, one or 2 key "wow" features, etc.
The wow features I feel like are going to be in being able to buy gym passes online (and cancel them). Basically try and circumvent the terribly oppressive process of not being able to cancel your membership.