i just made that mistake. only certain new logitech peripheries are designed to use the new "unifying" receiver. I have a keyboard that came with the unifying receiver (the unifying receiver has a little orange logo on it that the other logitech receivers lack). I assumed I could just buy any mouse to couple with it. I receive the mouse today and sure enough, it requires the separate receiver that it came with. Luckily you can find a list of Logitech devices that work on the unifying USB receiver scheme here: http://www.amazon.com/gp/feature.html?docId=1000433301. The previous reviewer is incorrect that you have to buy a mouse and keyboard coupled together. You can buy a number of devices working on one receiver as long as they are certified to work on the unified brand.
Older m305 mice are not compatible with unifying receiver. Newer m305's that come in the mostly white package with green swirl in the middle are. they have the circuitry built-in, but don't come with a unifying receiver, you would need to get keyboard with one included.