To be completely honest, I haven't fudged a die roll in years. I play over VTT. 99% of all die rolls are done completely in the open, and even those that are "whispered" to myself as the GM are still stored in the transcript. Any fudging I might do would be in the "Oh, look that hit brough the baddie down to 1 hit point, ah screw it, he trips and falls on his sword and dies." Which is a bit of fudging I've done and seen done in many groups.
But fudge a die roll? I actually wouldn't know how.
That being said, I'm actually quite surprised by this thread. Raven Crowking (and others) has argued at length and quite vocally that DM's are the ultimate authority in a game. They should not feel that they have to change for the players or for the mechanics. They should be the masters of the game - with authority over the game, the mechanics and pretty much everything that happes at the table.
But, here, we see that the ultimate authority in his game is actually the dice. Talk about disempowering the DM. It's okay to change the rules, it's okay to over rule a player's wishes, but thou shalt not change a die roll? Ever? Since when do the dice know better what's going to be fun at the table than a good DM?
I mean, we change mechanics to make the game better (for our groups). We create house rules and campaign and setting rules to make our game better. We can tell players "no" whenever the whim hits us. Don't want elves in the game? Tell the player no. I know for a fact that Raven Crowking has argued this many, many times.
But, the DM's authority does apparently have limits. It is limited by the fall of the dice during play.
I'll admit, I play this way a lot of the times. But mostly because, for the past year or so anyway, I have played games where the players have a LOT of editorial control. My last D&D campaign pretty much took death off the table, so, fudging wasn't an issue there either.
But, I'm enough of a DM's authority advocate to say that yup, a DM should know whether a result is good for the game or not.