They're targeted at gamers, but they're fantastic even if you don't game. The device let's you assign keypresses, multi keypresses, macros, mouse actions - pretty much anything you want - to each of the keys. Best thing is you can set up profiles targeting different .exe programs and the device automatically switches based on which program is active. So my Visual Studio 2012 has a different profile to my Photoshop profile for example.
Here's my current Visual Studio 2012 profile (still only partially set up):
Couldn't live without mine anymore - on mine I have 'copy, paste & cut' mapped and find these especially useful because I am left handed and pressing CTRL + C/CTRL + V either means I have to let go of my mouse with my left hand, or instead use my right hand to press them which gives me wrist/finger strain. So, the G13 placed on the right side of my keyboard is a life saver.