In an April 2003 CrossFit Journal article on pullups, Greg Glassman says, "Every personal best pull-up is an event worthy of celebration. You're going to live to be 100 but you'll not get that many pull-ups, so treat the new ones like birthdays."
Looking at the rankings for max pull-ups, we notice that Chris Spealler has proven him wrong. He recently knocked out 106 without getting off the bar. His closest competitors are Josh Everett and Pat Barber with 65 each.