Takes me about 100 miles to warm up, so I don't do that many centuries on my own. The rides I'm training for usually benefit from more structured training and riding 100 miles is only good for keeping my weight down. There is one 100 mile ride near here that always kicks my butt, no matter how good my fitness is, so I usually try that every summer just to make myself feel like I need to work harder.

I only rode over 100 miles 12 times this year if you count the 750 miles I rode in 3 1/2 days as one ride