I checked through both of the sticky posts looking for this and didn't see anything about it...and it has been a curiosity of mine ever since I started hearing the GS boarding announcements but I never asked about before (and I'm new to FlyerTalk).

I know they get top priority in the pecking order for everything and can confirm 120 hrs in advance for 500 mile upgrades. A friend of mine asked reservations once about it and all they told him is that it's for high end passengers (including celebrities) and you have to be invited to join??

How do you get to be GS? Simply more flying? More full fare tickets? What additional benefits are there besides the ones I mentioned above?

I had heard many rumors over the years that there was a hidden, non publicized level above 1K for hard core travelers that fly over 200k or 300k miles per year. Is GS the revealing of the stealth level or something else?