I've been running a Great Pendragon Campaign for the last couple years over on Myth-Weavers. Due to the slow speed of PbP play, and the insertion of some PC-specific storylines, we have just made it to the end of 494, after nearly 3 years of play.

We are now actively recruiting new players (http://www.myth-weavers.com/showthread.php?t=205082), if you are interested in a long-running PbP campaign.

Looks interesting. But the scope of it is immense.
I've played once in a Labyrinth Lord PbP who hasn't lasted long and I've GMed two old school D&D games, with one lasting 4 months and the other is still going after 6 months. Don't know though if I could commit for something this big. However, it could be one of my only opportunity to ever play in the GPC as I seem to be the eternal GM with my gaming group.