Adamnreeves, that story is pretty inspirational, that's the trick, finding something you love and getting out there and doing it.
I used to love playing squash but haven't played for a good few years after my squash playing mates moved away. I love mountain biking and could easily spend all day out there having a laugh in the woods with the lads and it's sad when the sun goes down and we all have to pack up and go to the pub, we have an annual lads holiday to the Alps, last year it was Canada to ride Whistler, I rode 700 miles in 10 days round the country visiting mates in a uni holiday, just out of boredom and the love of cycling. The exercise and calorie burning is just an added bonus. It's just what you love, I can ride 100 miles in a day easily but couldn't run a mile without getting a stitch and having to stop, cycling's also shrank my achilles and running is hellishly painful in the morning.
If you focus too much on the exercise and calorie counting it becomes a chore. If your base your exercise on a social group or whether you're into a solo head clearing, meditative thing, either way as long as you enjoy it, you'll stick with it.