Ok I just bought a G400 one week ago (was very hard to find a reseller).
So... If you tried the MX518 after a Razer (whatever the one), you feel the smooth accuracy of the sensor and the nice weight and shape of the mouse.
I was very surprised about the MX518, a very great mouse.
I used a Copperhead (Razer) between my MX518 died.
Then I heard about the G400, the last one of this kind of mices.
I'm using it now without any drivers, the 3600 DPI aren't a fag (but maybe there is less "REAL" DPI for the purists), anyway this is very very smooth.
The USB poll rate is at 1ms I think, because you feel it instantly after plugged it (for example for shooting opponnent, I have less or no more "rail through", you know).
In fact, buying a new mouse for gaming isn't necesseary, you can be the master without all this stuff, but if you have 29.99€ to spend, your gaming experience with the G400 would be really more pleasant.
(Sorry for bad english, fast writing before I leave)
Feel free to ask me any questions you want about this mouse.

Greetings.

had this mouse since it got released an its been solid for me. Just like an mx518 but with a better feel. You'll understand when you use one