I haven't really read that much on d20 modern, but what is the benefit of firing on full auto? can you shoot more than you normally could a round? couldn't an uzi fire every round in its magazine in a single combat round?
It's used to target an area. Then everyone in that area (10 x 10) makes a reflex save DC 15 or take normal damage. One needs 10 bullets to perform this function.
It doesn't say. I looked under the autofire description, under the Burst Fire feat (becasue it's very similiar to autofire), and the table that lists what types of action are standard/move/full round. So, I guess you can do it multiple times assuming you have multiple attacks and plenty of ammo in your weapon.
For example, if I target a 10-by-10 area but an idiot stands between me and my target area, does that idiot gonna get hit, too? Will that idiot provide cover to those in the target in a direct line-of-sight between me and the target victim(s)?
Personally I would have thought autofire would have a cone shaped area of effect not just a 10' x 10' area. I can see where they got the idea from, if you consider machine-guns creating a 'beaten ground'. But most characters are going to be using these weapons reasonably close up where the trajectory of any round is effectively flat.