I'd be interested in hearing more about your experiences with it. I'm trying to get a game up and running in boston, and while I've run a bit of spirit of the century (same publisher, similar system) I'm a bit worried about how lethal the system looks.
Dresden Files is about as far from lethal as you can get from a system.
Lets take an average character, has 3 boxes of Physical Stress and no special qualities (such as regeneration or toughness--toughness grants more armor, and regeneration means wounds only need time to heal and heal faster).
Put them in some armor and give them a hand gun and 2 ranks of guns. Clone them.
Dude1 with gun shoots Dude2 with armor.
Dude1 rolls 4 dice* and gets ++o- (net +1).
Dude2 is taking a 1 (hits) + 2 (skill) + 2 (weapon) = 5 stress hit. Dude2 is wearing armor (3) so is actually taking a 2 stress hit (Dude2 also gets a dodge, but I'm omitting that for brevity). So he marks off the second stress box: ( )(x)( )
Dude2 returns fire (whom we'll skip)...
Dude1 shoots again, getting ++o- again, dealing another 2 stress hit. Dude2's stress track already has the 2nd box filled, so he fills the third. ( )(x)(x). And returns fire.
Dude1 shoots again, getting +++-, doing 3 stress. Dude2's box is already full, but he hasn't taken a mild consequence yet, so he does so, reducing the stress by 2. He takes on the aspect** of "Sprained Shoulder" (which will heal by the scene after next, stress goes away between scenes) and marks off his first stress box (x)(x)(x) and returns fire.
Dude1 fires again and gets +---, doing 1 stress. Dude2's track is full, and he's not willing to take a moderate wound (they several scenes to a full session to heal, if you get some medical care--serious take sessions to heal and the extreme wounds permanently effect your character). So he opts to be taken out.
Dude2 isn't dead! He's only out of the fight as he's not willing to risk his neck any farther.
*Dice are either +1, -1 or neutral, depending on the kind of dice your using. I think the system intends for using d6s with 1 and 2 being -1 and 5 and 6 being +1. But my group had a bunch of +/- arithmatic dice, so we used those (no +0 spots). A character always gets 4 dice.
**Aspects can be called out using fate points (or avoided). In this case, Dude1 could spend a fate point to gain a bonus against Dude2 by taking advantage of that shoulder.