From what I can tell, the key to these niche social networking sites (of which yours isn't exclusively one, but sort of is) is to find an existing network of people and replicate it online.
It seems like you've found a great application of this idea... especially if you have loads of potentially sticky customers coming to your site every so often to register for races. I don't use Facebook, but if I had to register for courses through it, I'd probably have an account sooner or later.
It seems like you've found a great application of this idea... especially if you have loads of potentially sticky customers coming to your site every so often to register for races. I don't use Facebook, but if I had to register for courses through it, I'd probably have an account sooner or later.