Found this on the C25K website:
Interesting (and a little suprising) that most people drop out around week 4 or 5. So all of you that are at week 6 - you've beaten the odds.
And those of you that are at week 3 - don't become a statistic - keep going and become a runner. It really does feel great to be able to run for, first of all, 20 minutes and then in Week 6, 25 minutes.