I recently got an ASUS G74SX as a replacement for my previous laptop, and I've been absolutely loving it. Native 1080p on the panel, 12 GB of RAM, Quad-core CPU, and a wonderfully backlit keyboard.

I didn't see any options to control the keyboard backlight, so after digging around for a bit in sysfs, I found this with the backlight off:

$ cat /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/brightness
0

So, setting it is as simple as (where $N is a number between 0 (off) and 3 (full brightness)):

$ sudo bash -c "echo $N > /sys/devices/platform/asus-nb-wmi/leds/asus\:\:kbd_backlight/brightness"

You can find a simple shell script for setting it, here.