My experience has been nothing but positive when it comes to this site created by Joe and David. I have been using it since it's inception (yellow board?), finally becoming a subscriber in 2003. Last year I re-upped for the 3-yr deal.
I originally was hooked by the unique Excel VBD Cheatsheet (created by Bruce Hendersen, I think) that could be gotten for free and used it for a couple of years before I found the Draft Dominator (by Hendersen). This tool (DD) alone is worth the subscription price, for sure. Not only that, through this message board I have learned how to look at the world of FF a lot differently than I originally did. The posters on this board are very intelligent and knowledgable. Some are idiots, but it's easy to spot those and move on.
I find that I don't use the site for the obvious FF knowledge, but for the rare bit of info that could give me a leg up on my competition. For instance....in each of the last 4 years I've managed to grab the top waiver wire WR (A. Boldin, S. Smith, N. Burleson, C. Henry, M. Colston) in my league. If not for FBG's alerting me to these relative unknowns (at the time,) I would not have been able to grab these guys. These player acquisitions helped propel my already strong team to the title game 3 straight years. I doubt highly that my team would have made it that far without them.
I'm not very good at condensing my thought's into a brief post, so trust me when I say there are many, many more reasons why this site is worth every single penny they charge. Other's here can be much more prolific when discussing all these reasons.
I hope this helps you decide.
Steve