I've been playing in Trollsmyth's Labyrinth Lord game for over a year now, and only recently got around to keeping reliable notes. Partly this is because it's a chat game: there are logs. So long as I keep track of how to spell people's names, I can just search the folder I keep all my logs in and get whatever I need out of them. Still, at a certain point, there's no real substitute for notes: tracking expeditions, recording treasure, and remembering what happened on what day all require pulling stuff out of those logs and putting them somewhere else.
Which I did only haphazardly for a long time because I wasn't clear on what information I needed. I wrote down a lot more than I needed to, which meant I was mostly ignoring my notes, which meant I stopped keeping them.
But then the solo game got complicated enough that I really needed some way to start keeping track of time; we had a couple of upcoming events that my character needed to keep on her radar, and a lot of stuff happening in the mean time. At this point I'd been playing for long enough that I had a pretty good idea of what kind of information I wanted to be able to refer back to--I'd thought "I wish I'd written [that specific thing] down" often enough to know what I needed.
So I made a calendar. This was made easier by the fact that the months in Doom & Tea Parties game are all exactly 28 days long, so I could put together one template and then just copy it. That turned out to be a fairly efficient way to keep track of how my character was spending her days, so I made one for the group game, too.
(The fact that Trollsmyth appeared to be keeping track of dates on post-it notes scattered all over his office had nothing to do with it, I swear. And sorry this is so horrifyingly blurry. Clicking on it should link you to a version you can actually read.)
This is actually a bit different from the calendar for the solo game. Each campaign has different information I need to track, and the format reflects that. My character is pretty much in one place all the time, so there's no "location" tab, but I do break out her days into "day" and "night." The main thing I need the calendar to manage in the group game is expeditions out into the wilderness, and the location tab lets me know at a glance how long each one has taken. The solo game doesn't have that requirement, but we play through more, so each day needs to be recorded in more detail. The last few in-game days for the solo game each covered four, five, or six sessions, so the "this happened to my character two days ago and me three months ago" problem is much more extreme.
It took me a ridiculously long time to figure out the best way to track this information, because I'm horrifically bad at figuring out what information I need to track (and what information I don't) but now that I have, I'm pretty happy with it. I'm probably going to use the spreadsheet calendar system a lot in the future, though of course I'll tweak it a bit to fit the needs of the particular campaign. That's really, I think, the most important thing to remember about note-taking and information tracking like this: as with many things, each campaign is different. Paying careful attention to the particular needs of the game, and letting it take its own shape, is important.