I'm doing Weight Watchers and ride between 650 and 1,000 mi/month. (I have two small kids, a wife and a 105 year old house. The bike sometimes has to sit idle.)
I started at 360 pounds this past winter and am down to 285ish. I lost three pant sizes. It isn't easy but it isn't too hard. I still drink every once in a while and I still eat enough food. (But I was never a big junk food guy. I got fat on good food not fast food.)
I'm not the first one up the hill but I've never quit, either.
I'm looking forward to my next century and I am already planning a ride from NY to RI for the fall.