Judging from the current thread on the subject, and previous threads on the subject, it seems that most people consider fudging, (usually by the DM), to be completely acceptable. One argument is that fudging can make the experience more fun.
What other games are there in which fudging by one or more participants is acceptable and fun?
I would imagine that fudging is acceptable in any cooperative or at least non-competitive game. An example that most people might be familiar with is 'take backs', when you play a game and a player makes a really bone headed move, it's often more fun for all participants to grant a 'take back' so that the game is not ruined by ending prematurely. This tends to occur in casual gaming of all sorts, and at pretty much all age levels especially when competitiveness is low within the group by choice or due to large differences in skill between the participants.
I would hold however that in RPGs, even though I've fudged a time or three in my DMing career that "makes the game more fun" is actually a pretty harsh restriction on when you can fudge:
a) Only when it doesn't show favoritism: For this reason, players aren't allowed to fudge, since they would be fudging on their own behalf. Likewise, a DM can't fudge to reward a favored player or punish a disfavored one.
b) Only when it isn't obvious: There are a lot of reasons why you can't let the players know when you fudge, from avoiding social contrivery because of the appearance of favoritism or cultivating an expectation of future fudging on the player's behalf and then withholding it, to avoiding the player's metagaming ("I'll do this risky thing because the DM is going to fudge for me."), keeping suspension of disbelief, and maintaining the tension of percieved risk. The upshot of this is you can fudge only rarely. If it's happening every session, something is wrong.
c) Only when it is compensating for bad luck or your own bad DMing: Fudging to get your own way is wrong. Fudging to stop players from doing something reasonable but unexpected is wrong. The only real reason to fudge is to prevent the game ending prematurely because of your own boneheaded design or incredible bad luck (monster rolls three 20's in a round, player fails a saving throw by rolling a 1). Virtually all of the time that means you are fudging to prevent an unpredictable and uninteresting player death. Saving an NPC from death is too much like showing yourself favoritism, IMO.