Caleb - How much time writing and preparing do you do for each Know Evil session?
Ummm...I like flowcharts a lot. Like...A LOT. So I design a Prezi with the plot hooks for a tier of the campaign, complete with arrows connecting interrelated adventures. I also animate the presentation to show what order the PC's tackled the previous tier's plothooks so I don't forget. Each tier takes me about 4-5 hours to plan out that way.
I use the Prezi to keep the big picture in my head. At the end of each session or group of sessions, I ask the guys what plothook they want to hit next. They decide, and then that's the scenario I write up.
Past that, there is a ton of variation. At this point, I've run a session-and-a-half based off a single drawing I made on a bit of scrap-paper while my kids were taking a test. I've also run single sessions that ate through 21 pages of typed material (single spaced). If I average up my page-count, it seems like I'm wringing a play session out of every 7 pages of typed material.
I'm know I'm doing a lot more work than necessary. I'll often write pages and pages of setting description just for my own edification; most of it never gets mentioned in the game. Or I'll spend an hour stating out a path to the objective that I'm fairly certain no one in the group will ever select. I think I do this because RPG stuff is a form of procrastination I never really feel guilty about ("It's not for ME; it's for the PLAYERS!"). It also might be the way I've chosen to play the game; I probably wouldn't do it if I didn't enjoy it.
Sorry, I'm getting off on a tangent....
For an EP scenario, 10 pages or so of material is a good size for a single, self-contained scenario of 3-4 hours. The setting is pretty dense and encourages realism (they aren't going to get a quest from a Tavern/ why rescue the princess when we can restore from backup?/ etc) so including some of the Act I and II stuff that gets cut in most RPG's means the actual writing requires a bit more work. Ten pages will give your PC's enough setting description to give them room to play, some investigative footwork, and an encounter or two. Anything more than that and you are probably looking at a two-parter.
I write on my day off and try to do two or three sessions worth of stuff at a shot. That takes me...4-5 hours?
So I guess I do a little under 2 hours of work per session. There are a lot of resources out there to speed things up. NPC files are fucking essential; I would not GM without that PDF. Sunward is the best supplement so far (though Gatecrashing will always hold a place in my part) because it gives the best idea of how the factions interact. And go on the EP forums because there is a ton of stuff you can steal and plug in.
I'm finding that things are getting easier the further we get along, but then again, I'm consciously trying to improvise more and plan less. In a campaign, established PC's can pull a lot of the narrative weight once they get their legs under them. I did a shit-ton of planning up front for the Luna finale, but I'd say the last 6-7 hours of gameplay were entirely player-driven. The Earth tier is starting with a pregen setting (The Stars Our Destination) where we are just taking care of player subplots. So I suspect things get less labour intensive the longer you play, but I'm not sure. Once I relax myself into writing and running a game I'm not proud of, I guess I'll have found my equilibrium.
Sorry...I rambled on. IN SUMMATION: I'm the new guy, but I know what works for me. Ross could probably give you better idea of how much work should go into a single session.
Anyway, thanks for the interest Salkovich!