Group #1: 6 years. Technically speaking, the group started close to 14 years ago, back in high school. We stopped playing for 5 or so years, and then most of us got back into the hobby. And then one-by-one we started dropping off again. And then it was just me, and one of my best friends from high school. My wife joined, and then we recruited 2 other guys. Even though 2 of us carried over from that first incarnation, I really feel like the current incarnation of me, my friend from H.S., my wife, the 2 guys we recruited, and the 2 guys we've added since then is a different, solid, stable group. So, 6 years.
Group #2 is going on 2 years old. Good group of guys, though the games tend to be a little more rules-heavy than I prefer. It works though.