I've run a Planescape campaign since 2001, starting as 2E, morphing into 3E, and now firmly entrenched in 3.5E. Recently, it's moved to a message board game, as the players are scattered throughout the U.S. and the world, and we can't coordinate a time where we can all meet to play. You can check out the game thread
here if interested.
I am also a fellow author of Shemeska's, having written the Athar and Ring-Giver entries over at Planewalker.com, as well as faction prestige classes for 3E and 3.5E. I'm also a fan of the affiliation rules, and I'm working on the factions as affiliations at this time. (You can find the prestige classes and affiliation
here.)
I mention all that because, in the five years my players have been in my game, they have taken no interest in the factions. The factions are there. They have met factotums as NPCs. They have learned of their philosophies, goals, and influences. And they have chosen to remain distanced from them. Despite all my work.
All of my campaign has been pre-Faction War, as I'm building up to that adventure (mostly likely adapted to epic-level play). Currently, the heroes are going through
The Great Modron March, to be followed by
Dead Gods. I want the players and the characters to witness the power of belief and the drastic changes they can have on reality. So even though the players have no investment in the factions by way of their characters, the factions play a major part in the overarching campaign plot. I pray all my work will not be in vain.