I participate in cyclocross races and some short track mountain bike stuff, but I'm more of a roving obstacle than a racer. To the extent that I train, most of it is just variations in how I ride my commute. Depending on what I want to work on I'll choose a route with more hills or longer stretches without traffic control devices. Generally, I'm not disciplined enough to improve much, but I'm also not terribly worried about my results so that kind of works out.