Just rootling about on this site - found in the directory that you can list all the graduates - there are now 629. According to the heading, "Graduate are people who work for Couch to 5K" - I suppose in effect you do work for c25k, because you all promote how effective it is!
And there are many others who have done the programme without registering on here - I know someone at work who did it last year, which is how I first heard about it.