I'm currently in a 3EdD&D campaign (homebrew) that has been running since shortly after the game's release- a 2Ed campaign was being converted to 3Ed when it imploded... Its the only active campaign we have.
However, the reason I play 3Ed exclusively is because the guys I game with don't want to convert ot 3.5 or learn any other systems. We've been playing D&D almost exclusively since 1996 (there was a short-lived Rifts campaign, shelved 2 or more years ago).
Personally, I prefer HERO, and would desperately love to play something (anything) besides another fantasy game. I even let my last campaign die when a few players (in a different, overlapping group) had to move away, rather than bring in new players. In part, its burnout, I know. However, its also a simple desire for variation.
In my previous group (1991-1994), everyone was responsible for running a campaign, to keep things fresh and make sure that everyone could play something they loved. As a result, I ran a HERO game (Supers in 1900) and a Rifts campaign, and we also had 1 D&D campaign, 1 Paranoia campaign, 1 MechWarrior campaign, 1 Mekton campaign, another Rifts campaign, another HERO campaign, several GURPS campaigns (including a playtest for GURPS: Vampire- VIVA Major Mosquito!!!) and a playtest for Aces.
In contrast, I can't even interest my current group in a D20 Modern Horror/Fantasy campaign I'm designing.