The core concept for the Ghostwalk proposal was, "If your character dies, you can continue playing immediately as the ghost of your PC."
Well, this was one of my problems trying to shoehorn it into my existing campaign. (Note: I wanted to use it as a "second chance" for characters in a high level campaign; if you die then you can return as a ghost, assuming you can't be Raised. If you die as a ghost, oh well. This to explain where I am coming from.)
Anyway, in Ghostwalk when a dead PC comes back at first he is ethereal. If he doesn't like being ethereal, he should be able to transition to incorporeal within a couple of minutes. Being incorporeal (or ethereal) for long periods of time will cause huge headaches for the DM, especially as I expected my scouting classes (monk & rogue) to be more likely to decide to "stay dead" as opposed to fighters and mages.
In the long run though, I am not sure that being incorporeal is that much fun for a PC. So once the fun wears off, they will try to transition to fully manifested. Which is a lot like being alive again. I kinda got stuck here and decided I couldn't really tweak these rules into something I wanted for my campaign, so I put the idea on the back burner.
This is what I was getting at when I said that the city of Manifest is almost required to play Ghostwalk -- I am pretty sure the ghost rules (even including the classes and feats) are not enough by themselves to make players stay ghosts for long. If you like the idea of Manifest and base your campaign around it, that's a different matter, and I bet that's the way to go to get the most use out of the book.
I am still curious about people's experiences though; especially anyone who was in a campaign where some fraction of the players decided to be incorporeal.
-edit- ... or if anyone has ideas about how to run ghosts as a "second chance" for dead PCs, I am interested in that especially.