Rolls that are hidden from the PC's

Pathfinder: Sense Motive, Knowledge, Stealth, or simple Perception rolls are all examples of skill rolls that a DM doesn't want his players to know the results of. Everyone is on alert when the DM asks for a perception roll. Even better is if there was a dialog box where you could have multiple preset rolls go off and keep the game going without the players knowing whats going on. Sitting at my desk at home, I could just as easily roll some dice at my desk and no one would be the wiser, but I would find it best to keep everthing on the screen. My username is Brian R., I simply had trouble logging in.

couldnt you just do a /gm roll so that only you see it

I just roll in the open. I just don't label what they roll is.

And adding to this... I just roll sometimes without the results having any meaning. I might say "Hmm... that's going to be interesting...." or something like that...

I tried rolling secretly (made myself a GMrolls macro that said: /gr 5d20 Dice roll ominously behind the DM screen. I just felt that players were missing WHY I did not tell them things. I'd rather they get the meta knowledge that their character is working with an imperfect view of the world and see their roles, and know when they are due explanation and when I can't give it to them.

that's awesome, shawn !

The /gmroll option is a great way to deal with things like this. I would feel odd modifying the players rolls, as I would never do this at a real table without just telling them to re-roll for some reason or another. If that wasn't enough, then the smoky hand of the GM can just explain what happened and the players are left to figure out why. This can easily lead to a fun plot twist for your players if you do it right, and keeps the sacredness of the random number generator. Also, do you really want to deal with a player deciding that all his crit fails were the GM being mean to him?