Notes!

So the issue of my notes for sessions and play has come up, and I think it's a pretty important topic to gaming for everyone.

When I gamemaster, I expect to write up one page for every 4-5 hours of play. Then during actual play I expect to write up another page of notes. I also do a few pages to cover the larger area. Sometimes this is by region or by level.
The pre-game notes include people and places. Rough maps are usually in there. I also usually include one or two combat encounters they might come into in that area. Generally things that are likely to come up during gameplay. I want these on paper and ready to go right away whenever possible.
The post-game notes are usually all sorts of random things that come up. Things like XP gain, big expenses, things I need to adjust, etc. In my previous 4e game this included things about re-balancing magic item distribution, boosting the PCs (I was in talks with a player about a major character rebuild before the game ended), battle information and all sorts of random stuff. Then there's the stuff about what the players did. Examples in my previous 4e game were things like trying to kill each other in a bar fight, helping out the guild overseer, finding a hidden artifact, etc. Things that might come back to help or hinder the players that will need to be remembered.
The larger section is usually more general things, a few pre-planned combats I can drop in just in case I use all my other prepped combats or can't use them for some reason. For the 4th edition game, because of the huge reliance of having an exact make up of magic weapons at certain levels, I also found myself keeping a record of all the magic items the players have. This made one of my least favorite parts of the game a little easier to manage. Nothing against the having magic items, but having them at certain levels and needing them to be certain pieces is a very real headache. Maps of the region the players will be in get included in these notes too. Experience plans, etc. Not to mention to overall plan for this section of the game.
There's also of course the campaign notes themselves. Things like how I plan to handle character building, the overall story, etc.

As a player, the importance of notes is just as important. I usually have a single page of notes as a play per 4-5 hour session. There may be more or less depending on what happens and how involved it is.
I try and make sketches of random things, just so I have a clear image. I make notes of goals and plans. I really try to avoid writing a log of what happened, because in the long run, that's fairly unimportant to me. I may later type out a narrative of what happened, but that's more for memory and entertainment than actual use.
I also find that if I make notes of my characters abilities I can figure out what is actually useful vs what just sounds useful.
Finally I make notes of how I want to drive my character's story forward and how I can do that. I'll usually write a little back story covering a brief part of this or explaining something. I like writing this out because it make it more concrete (and again, for memory).