some of you can confirm that this Microsoft technology really can't do its job as claimed when it comes to cotton surfaces?
In my recent experience, based only on ordinary use rather than any exhaustive A/B comparison on numerous kinds of surfaces, BlueTrack mice from Microsoft (e.g. Wireless Mobile Mouse 3500) do not track any better than Logitech mice that work with invisible infrared light (e.g. m317, m325). I just tried a 317 and 325 on various plain cotton, including a bed sheet; they are fine.
BlueTrack mice have terrible battery life from powering that bright blue LED. You can extend that life by turning them off, but it doesn't help that much (it reduces the problem from "really bad" to "bad"), and the switch is too flimsy to last much more than a year of regular use. Before you know it, you will be fiddling with the switch to get the mouse to power up. At which point, ironically, you will be relying on that blue illumination as an indicator whether the power switch is making contact.
Given that mice can be designed to perform excellently with infrared illumination not visible to the human eye, using blue LEDs is a perfect example of a "solution in search of a problem".
Because of the battery life issue, it's moot whether or not these mice track well. Ideally, they should be left to track the interior surface of their unopened factory packaging.