I've been at it on the Flex Plan for about 18 weeks. It has been PAINFULLY slow (only losing 9.6 lbs since the summer!) and I am thinking about switching to Core next week.
I've done it in the past. I'm not current doing it on a very strict basis, nor do I attend meetings any more, but I generally have a pretty good idea of how many points I take in a day. lost about 45 lbs doing it. I've kept almost all of it off for over two years - give or take 3 -4 pounds.
Core plan. Slow but steady.
Just watch what you eat and work out. That helps.
Found a very good food site last night; was looking up Swiss Chard. http://whfoods.org/