No I am not a member. I've never heard of such a thing and the cynical side of me feels this is fishy.
They have to make money somewhere. What is the yearly fee? Are you guaranteed any spots at big events that you actually might be interested in? How many spots are you guaranteed? What is the justification of the membership fee if you are not guaranteed a certain number of seats?
Sounds like a great sales pitch but you may pay a yearly fee and never be called... are you willing to take that risk? They are counting on people to not be available to go to the events when called, etc... therefore they pocket all the membership fees.
I would not sign up for something like this. It just sounds too gimmicky. I'd use the money they want for the yearly fee to plan what events I wanted to go see and do and know I have a guaranteed seat.
Let us know if you go for it!