Get Imba. That's what it says on the side of the Razer Naga packaging. If you don't know what that means (it's short for imbalanced), the Naga probably isn't for you. But, if that sounds like all kinds of win, read on.
The Naga's main selling point is the huge, twelve button grid, located where other mice usually just have back/forward buttons. To accommodate the grid, the mouse is slightly fatter on the left side, resulting in a sloping grip that actually provides a really comfortable, ergonomic feel. It does, however, mean that the Naga is for right-handers only.
This grid by default, is mapped to the '1' through '=' keys on the top row of your keyboard, and is designed for games like World of Warcraft and Warhammer Online, where keys are commonly used to activate abilities so that you don't have to mess around with trivial things like key bindings anymore.
Obviously, you don't need a special mouse just to hit those keys (unless you really do want to play one handed), as most people on a standard WASD setup should be able to hit at least half of them without any serious finger stretching. So, on the bottom of the mouse you'll find a switch that lets you change the grid's mapping to the numpad instead. This is far more useful, but will require some in-game configuration to get your abilities set up.
Unfortunately, other than those two configurations, the grid can't be re-mapped to any other keys, so for games that force you to use F1 to F12, or the letter keys, the Naga won't work as intended
The grid itself is laid out like a calculator (or cell phone) with 1, 2, 3 at the top and 10, 11, 12 at the bottom. The buttons are well sized, so you're unlikely to accidentally mash multiple keys at the same time unless you have really fat fingers.
It did take some getting used to though. While it was relatively easy to hit the corner buttons, you'll have to feel your way around to hit the ones in the middle row, and the last row is far too low and will require some uncomfortable thumb gymnastics to reach.
We ended up using just five of the twelve buttons (1, 2, 3, 4 and 7 being the easiest and most comfortable to hit), which makes us wish Razer had just made a much more sensible, six button grid instead. Even so, this works decently and combined with Shift and Control modifiers, it gave easy access to 15 more key bindings than usual. If you're dexterous enough, using up to nine of the buttons seem possible, but hardly the full twelve.
Overall, unless you have a real burning desire to play one-handed, the amount of time you would need to invest into becoming a pro with the Naga seems like it would be better spent elsewhere. However, if you're just looking for a couple of extra hotkeys over the competition, the Naga will give you that slight edge. But is it 'imba'? Probably not.