I've done it in TT, when my dice were on fire and I kept rolling nat 20's, well, I didn't feel like total PK'ing the party that night and so some crit hits became misses. I think there requires some trust in the group with the DM/ST/GM in order to create a good story.
On a MU* though, I fudge /nothing/. All rolls are out in the open because I cannot allow any sort of favoritism to be present. I can't pull my punches in one situation and not the next because it's not the same environment and you never know when you're going to get the same collection of individuals again, even if it's for a continuation plot/session.
On a MU* I believe it should be by the rules, whatever those rules are.
I even put in code so that people can set their own verification code for dice rolls so that people can't spoof rolls as the verification would be wrong and people would know without having to be set nospoof.
The reason I feel that way is because it is the /only/ way to be fair to everyone, as impartial as possible. If the rules say something, then that's what it /is/. Period. Otherwise you cannot guarantee anything remotely resembling fairness to every player.
