How about most of the rules... I used to have the 2.0 rules down... ask me anything... I could almost quote the rule verbatim, and the players respected that.
Same group 10 years later and I find that we look up the rules constantly, and for easy things too. What's a climb check when using rope, is a 5 or +5. How many images is it for Mirror Image? (and what is the AC of those images). How does trip differ from disarm? Fighting defensively, what is that (standard or full-round)? Aid another, the DC is 10, right?
Most of the time I remember, but then it comes up in game, I make the ruling (based on what I'm pretty sure the rules is), and then we look it up anyway. I get about 90-some out of 100... but we are always looking it up. The players don't remember, but they do remember that there is a rule somewhere....
I make my players look rules up or they have to go with my ruling... But this leads to a few problems when I make a judgment on the fly, just to have Joe Fighter, NO, Wally Wizard say, "actually, it says on page x that the spell blah, blah, blah..." 5 minutes after I made the ruling. I (almost) always stick to the ruling, but in cases were PC death might be involved I will always reverse the decision if someone has died.
Either way, I'm constantly looking up the rules now. (easily done with the SRD on the laptop)
Aluvial