July 2000, when we moved to Illinois. (New York's Time Warner Cable added it about a month or two after we left, of course.)
I had been exposed to it before - I had someone working for me who got a few tryout weekends on her cable system, so I got tapes from just before The Dark Period, during The Dark Period, and just after it ended.
We're buying a house and moving in two months - debating on whether or not we want to spend the extra $10 a month for the digital tier to keep GSN. We probably will (my wife likes BBC America, and there will be some shows for our son on that tier as well), but it's not like I watch all that often anymore.