Here was my experience:
Back about a year ago I did this because my mouse was actually defective. It didn't skip around, but was tempermental when right clicking. I sent in my fax, and they very promptly shipped me a new one.
I never got around to opening the package because I got a new mouse at work. However, now while at a new job, I opened up the package and used the mouse for about 2 months before it failed to left click properly (it registered double clicks when I only single clicked).
I called teh generic MS technical support number and they ran me around in circles a bunch. The Indian lady (and then man) were obviously just reading some scripted crap, although you could tell their pronunciation was good, but they could hardly understand me if I spoke beyond a 4th grade level.
...And that is what brought me here...I called the supplemental parts number listed above, and the very friendly Canadian woman on the line very promptly arranged for me to have a new mouse shipped out.
So, I extend my thanks to the good people here at Anandtech and to MS for getting me a new mouse. You guys have never let me down!