Another idea that Vivictus' thread brings up is the concept of "DM Cheating" - one that has been debated on this board many times in the past. Some gamers consider it "cheating" if a DM does not abide by the results of each and every roll that is made; others do not take as strict an approach on this.
In our games, I have been alternating between rolling in the open, versus rolling behind a screen, with the emphasis towards open rolls. However, I also don't consider it cheating if a DM uses closed rolls, because the DM is the one in ultimate control of the environment; the players hear and see what the DM tells them they do. If a DM wishes to "cheat" in such a way that he feels betters the game, by either fudging a roll, or by simply decreeing what a roll is, and the players are still enjoying themselves with the results, then the game is bettered as a result. Looking at it another way, the DM has control of the AC's & skill totals of opponents, and the DC's of tasks, so having control of the opponents' die rolls is not that much of a stretch.
The player's, on the other hand, do not have control of the DC's of tasks, nor control of their opponents' proficiency; part of the fun of the game to me is the challenge of making do with the die rolls at hand, and winning the day despite bad fortune. That said, the gaming group may prefer a house rule where the players also have a number of "cheats" at their disposal; in fact, games such as Spycraft, d20 Modern, and the new Savage Worlds game assume it right into the system!
Impartiality is essential to a DM; however, making sure that players are having a good time, and not unfairly shafted by persistant bad luck is also essential to good DM'ing. I have learned many lessons in my DM'ing, and the most important one is that people do not drive from 30 minutes to an hour and a half to a game, in order to blow 15 die rolls in a row, fail in the end, and watch other players have fun because they can roll well and you can't. It pays sometimes to obey the spirit of the law, rather than its letter, and it comes under the balancing act of being a good DM.