I've been on my fixed gear commuter for almost a year now. I ride it as often as possible, and it's taken me many nights in the garage to learn to trackstand. I can pull it off for as long as I like in the safety of my garage, but find it a lot more difficult on the street. It's definitely easier with my left foot forward, but I'm starting to stick it too the other way around. It's getting easier and more natural, so I imagine with practice I'm sure it will become second nature. I'm not sure it's entirely "useful," it just feels so neat to be able to do it, cool points aside and all...