Making notes on your opponents in SNGs is very important. Whilst stats from poker software such as Holdem Manager are great, note-taking allows you to record things like time-tells (e.g. if a player has a habit of insta-checking when weak, for example).
Note-taking is valuable whether your sit n go opponent is multi-tabling, or just a regular who only plays at weekends. It allows you to store away knowledge which you can then use to exploit your poker opponents.
What to record in an opponents notes
So with that in mind, what sort of thing should you record on notes? Here are the ones I would normally make
1) Time-tells - e.g. do they insta-check when they're weak, or when they're trying to appear weak and trap you? Do they draw things out and use time-bank when they're strong? Any of these things you see, note them down. I always like to record how many times I've seen them do this - the more they do it, the more of a habit is and therefore the more you can rely on it.
Example note on time-tells: "Insta-checks when weak (x2)"
2) Profiting or not? This should be used in conjunction with color-coding your SNG opponents . As well as noting down if they're a profiting player, I often make a note of the date I put the note on. Sometimes a player early in their career can hit a heater but then two months later be a losing fish.
Example note on profiting - "+5% ROI but small sample. 01/05/11"
3) Notes on hand ranges - as well as looking at the cards when they're shown, be sure to use the 'last hand' facility in your poker client to look at the cards your opponent is playing. This will allow you to get a feel for their range. Are they limping junk like J2o in the first hand of the SNG, calling a raise with Qts early on etc.? It's also good to record what their raising range is.
Example note on hand ranges - "limped Q5s from button 1st hand. Raises any ace late position"
4) Notes on what their 'moves' mean - be sure to write down any time you get an idea of what each 'move' means. What does it mean when they min-raise post flop? Are they strong or bluffing with air? Do they always flat call with the nuts? For ages I struggled against a leaderboard regular in the 6maxes, before one evening spending an hour watching him play. One of the 'move tells' I picked up was that he only shoved post flop with the nuts or a very strong hand. Using this knowledge meant I could play more effectively against him.
Example note on move tells - "Only 3-bets pre with QQ+", "min-raise on turn - steal/bluff"
5) General/personality notes - This will be just a quick note backing up what you'll be (or should be) seeing on your HUD from SNG software like Holdem Manager. Keep it simple e.g. "LAG", "TAG", etc. I also note down if the player displays any impatience. Many one-table regulars get driven crazy by regs timing down and tilt as a result. If you see this impatience (most commonly by them putting abusive comments in the chat box), use this to your advantage by timing down in every hand with that sit n go opponent.
Example note on general/personality tells - "LAG, hates being timed down."
Summary
Use the note facility on every player you come across if you can. It only takes a few seconds to do but can be the difference between cashing or not. Be sure to do so inc onjunction with color-coding your poker opponents and the HUD of Holdem Manager where you can.