Perfect Control
When you move your mouse it may result in turning your viewpoint in an FPS game, moving the cursor in an RTS game, or something else like rotating a tank turret. In each case the importance of using a mouse is the proportionate response. If you move the mouse slowly you expect to turn slowly or the cursor to scroll slowly. If you move quickly you want to be turning faster or the cursor to move quickly across the screen. If someone creeps up behind you in a game you want to be able to make a wild flick of the mouse to face your opponent quickly and return fire. The ideal mouse response is a linear one, where moving the mouse twice as fast results in a response of "twice as much". I define Perfect Control as the top speed up to which the mouse performs exactly as it should.
Malfunction Speed
Another important factor in choosing a mouse is the fastest speed you can move before it gives up and decides to fire the next rocket at your feet. I call this the Malfunction Speed, where the mouse loses control and effectively stops working. When you flick your mouse beyond the Malfunction Speed, anything can happen. You may either end up looking in any random direction or just find you haven't turned around at all. All optical and laser mice must have a Malfunction Speed, so we want it to be as high as possible so you don't notice it.
Dots-per-inch
With a printer, the DPI (dots per inch) tells you how well the printer can translate information from the computer onto paper. For a mouse, the DPI value tells you how well the mouse can translate your hand movements to the computer. It would seem that a higher DPI would theoretically mean a better mouse? Before you run out to buy the highest DPI mouse we should think carefully about how much DPI is actually useful on a computer that spends most of its time displaying images made up of pixels. I discuss this a little more on the next page.
http://www.esreality.com/?a=longpost&id=1265679&page=1
