The charger that comes with the S3 outputs 1.0 amp (5V), and my old Galaxy S1 Captivate came with a 0.7amp charger. Both are better than the measily 0.5amps that most computer USB ports output, which is barely enough juice for the phone to break even (let alone charge) when you're using your phone with the display brightness at 100%. Obviously the fastest way to charge is with the phone off, or a spare battery, but most of us don't do that.
How many of you are using an aftermarket 2amp usb wall charger without issue, and have you measured how much faster it charges? Also, will this faster charging reduce the S3's battery life, or is it within tolerances and Samsung just cheaped out on the included A/C charger?
As long as it's safe, I'm thinking about buying one of these $10 2amp chargers off amazon...
UPDATE: I read elsewhere that a 2amp charger can't really hurt your phone because there's obviously "smart" circuitry inside that limits the current anyway. If it really is smart, then the upside to 2amps SHOULD BE that when you're charging with the screen on @ 100% brightness, that more juice goes to the battery with the "extra" going to the display, instead of subtracting from what the battery gets.
Short answer: the two amp charger won't hurt the phone, plus it also is highly unlikely it will charge any faster on this particular phone.
The preceding discussion applies to "dumb" chargers and batteries (which ShannonPricePhoto pointed to a few posts ago). Increasing the charge voltage causes the battery to draw more current depending on the state of charge. The trick is we have both a smart charger and a smart battery in his phone. Lithium-ion batteries actually contain circuitry to prevent them from being overcharged inside the battery.
The cell phone industry has agreed on a worldwide standard cell phone charger as follows: it uses a micro USB connector (not a mini USB) they all charge at 5 V, the smart controller for charging the battery is inside the phone, and it determines how much voltage the battery receives during the charging cycle. (Not the charger, like a dumb charger used to charge a car battery, which changes its output voltage)
The standard allows for charger supplies ranging from 300 milliamps to 1 amp, and the phone can actually inquire what the capacity of the charger is through the USB data line.
Reading the standard makes me wonder if using the larger charger would allow the phone to take advantage of the full 2 amp capacity of the charger. One post indicated that older devices that were not covered by the cell phone standard may likely have charged quicker with a two amp charger, but I seriously doubt your phone will because it wasn't designed to do so. This however is an educated guess. One way to really find out is get two chargers and compare by measuring the actual current?
For even more reading
The first website discusses the standard mobile phone charger, the second discusses batteries.
Universal Serial Bus - Wikipedia, the free encyclopedia
battery myths vs battery facts - free information to help you learn the difference