@figment: There's a couple of things that sets high end gamer mice apart from cheaper mice. The one thing that isn't particularly useful is the ultra high resolution. They're up to 5600DPI now (if not higher), which only makes the mouse ultra sensitive (lots of cursor movement for a very small mouse movement). There's also the USB polling rate, which is 125Hz by default, which is "good enough", but 500Hz offers a noticeable improvement (slightly smoother, more responsive movement). The polling rate only goes up to 1000Hz (which actually isn't noticeably better than 500Hz), but this isn't the cause of the high frequency sound that some of these mice emit. The cause is simply a design decision from (mainly) Logitech, which affects even the lower end mice:
Past information on this site stated the problem was with the IR/LED transmitter used in handling scroll wheel functionality: this is not the case, but the IR/LED transmitter does play a role with regards to the issue. The source of the noise is a ceramic capacitor on the the mini-PCB of all of these mice. The mini-PCB is what holds the left/right/middle buttons, as well as the scroll wheel, in addition to some very basic circuitry.
A technical description of the problem from the individual who tracked it down:
The problem isn't terribly uncommon - ceramic caps have an awful lot of good qualities. For a number of applications, properly rated ceramic caps are pretty much the ideal choice. The problem is that if there is enough voltage ripple on a ceramic cap, it will physically "ring" (Google for "ceramic capacitor microphonics"). The real kicker here is that whoever designed this for Logitech decided to pulse the wheel encoder LED at 5KHz, and due to the magic of frequency multiplication, we end up with noise at the 3rd harmonic, 15KHz which is high enough to only enough to drive some small fraction of the general population nuts. ... If Logitech were to change the sampling frequency up by 20% or more, or change the capacitor type, or just stop pulsing the thing and eat the extra couple mW of power dissipation, this issue would go away.