First, there are 3 different plans, $14, $25 and $39 a month. Not everyone will do the $39 a month plan.
I did the introductory 2 week period. It has a lot of good information on earning miles and redeeming miles. This would be a good for newbies or people who don't have time to search the FT forums. But, it is overpriced. I'm good with the $1 I spent for the trail, but I only saw 1 thing on there that I hadn't seen anywhere else.