I'm really surprised at how many people support the Fate/Fudge die system as seen in DFRPG (Dresden Files RPG). In my group of eight or so people, none of us like the die system, and we're familiar with most of the systems out there. It adds more complexity to a single dice system, and for what benefit? With aspects and fate points, you can almost always "pay" to have a higher result than you roll. Additionally, you can roll into the negatives, effectively undoing the skills of you character. Finally, the average of the die roll is a 0, so as a rule your die roll has no effect. And this is when you're attempting against defenses that are relatively high and so on.
It's a bell curve system. Getting a +4 on the fudge dice is a really impressive thing and statistically shouldn't happen that often, given how big the difference is between a Mediocre (+0) and a Great (+4) result is. The distribution means that most of the time, you can expect to succeed on a task with a difficulty equal to your skill, you're likely to need to spend a fate point on one with a difficulty one higher, and you'll almost certainly need one for a difficulty of two higher. That makes it easier for the GM to assign difficulties to tasks without worrying that the RNG will vary wildly like it does in a d20 system, where you're as likely to perform at an average level as you are to make a superhuman effort, and as likely as you are to make a half-assed attempt.
Negative die results might seem odd, but they're actually the same thing as making the curve go from 0 to 8 and bumping up the difficulty by 4 points. The curve is just centered around zero here because that plays more nicely with the math and looks better on paper. Besides, people can and do perform worse than their potential in real life because of all kinds of crazy circumstances. Automatic success is covered when your skill is 4 points higher than the difficulty (which is pretty incredible) or you burn fate points to add to your roll, which is fine because automatic success should be reserved for mundane situations (which don't normally merit a check because they are boring) or simple tasks performed under stress by professionals (which are rarer).
Having the average be zero, again, is helpful because it gives the GM a good idea of what his target numbers should be. It also reduces randomness, which tends to favor the players. As for high defenses, you can get around those by playing with maneuvers and temporary aspects, or in the case of certain supernatural monsters, satisfying the Catch.