No real system other than a few acronyms... I do take note of the players who play weak aces and suited cards early in SNGs (at least until 6 to 8 tables... kind of gets hard after that!) anything which either helps define their bubble calling range or their ability to fold to a big reraise in the mid-game is key in a SNG...

For MTTs I also note raise / fold betting lines (ie what bets might show weakness), ace=x hands played, any unusual bet sizes and also how people play draws... would probably benefit from a proper system for doing this but to be honest I'm not that disciplined!!

Cheers, Mark