Long distance running is my main hobby outside of work -- work should really be considered both my occupation AND a hobby. I run mainly because I enjoy it. Beyond that, it really helps me keep my life balanced. Having about an hour a day all to myself without interruptions is completely zen-like.

While competing in events is not necessary to keep running, it's so much fun and motivating. I've been recently running marathons and have grown fond of them even though I find the half marathon to be a lot more enjoyable and reasonable.