I always hate when a player can roll a Knowledge, Perception, Sense Motive, etc. check and know (or assume) they failed by rolling low. It can definitely influence character actions, and most of the time it is just metagaming.
I made a little excel table numbered 1-20 with random values, also 1-20, in the next column. The randomized column would represent the actualy roll values for certain checks. They can easily be regenerated, so a player can't catch on to what a good roll is.
I don't want to implement it for combat. I feel like a player might roll a 20, and be upset if the corresponding value is a 1 or something.
I could see it being useful as a DM to "fudge the rolls" if the players are just having a terrible string of luck though. Overall, I think it would hurt the game more than help it to use for attacking in combat.
Also, I most likely wouldn't use this for skills that your character would know succeeded or not (climb or disable device checks for instance). A character would know if he climbed a wall or not, and would be able to gauge the difficulty.
However, I could see using it for saves made against effects that don't onset immediately, or for saves vs illusions. Especially the latter. Also, as mentioned above, skill checks that a character wouldn't necessarily know failed.
Now, I have not brought up the idea or implemented it yet, but how would you feel about this as a player? Does it hurt the game in a way I am not aware? I of course can make secret rolls for some checks that are passive (like a perception check to hear something that the player isn't actively listening for), but if the player is actively making a check (for instance, a bluff), do you think this is a good or bad solution?
Isn't it much more usual for the GM to make those rolls for the player in secret? I've done that plenty of times:
Player: "Do I think he's lying?"
Me: "What's your Sense Motive bonus?"
Player: "+14, with the buffs I have up right now."
Me (rolling in secret): "You think he's being honest, and you know you're a pretty good judge of character."
I guess I was overthinking it! lol
However, it'd be a decent alternative for player's that like to roll for themselves.
There are a few elaborate dice-boxes available on the market that would allow your player to drop in his die and yet not see the result. Dice purists who don't want others rolling for them or don't want other people interfering with their mojo by touching their dice could look into it.
(Personally I just roll for 'em. I keep a chart of the characters' Perception, Sense Motive, Fortitude and Will saves handy since those are the four rolls that might give something away if I ask for the modifier just before a secret roll: asking for a Knowledge modifier doesn't give away much... except in the case of shapeshifters or something.)
That would be worth looking into. Thanks!