Yeah, I read a review about it tracking bad where the guy was moaning about it wouldn't track while he was in his bed. It wouldn't track on the blanket, or even his notepad.
I use the mouse on a desk. I have never had an issue with it tracking poorly or getting laggy, period. I can use it on my desktop or on a mouse pad. It will not work on reflective or glass surfaces. This is the nature of a laser mouse. If you need something that can track on anything, then you need one of those that has both optical and laser for tracking. Logitech has one they advertise can even track on shag carpet or glass.
You probably won't be tracking well if you use your pants leg to navigate your mouse. If that's your situation, get a touch pad instead of a mouse. For tracking on a non-glass, non-reflective hard surface or decent quality mouse pad (not the dollar store mouse pads), then this mouse just can't be beat. I got a mouse pad from Walmart for $5 to keep the bottom of the mouse from getting scratched on the desk. Don't really need it other than that.
I have been using this mouse for over a year and am extremely pleased with the performance. The battery life is still quite strong as well, showing that I still have over 900 Days of battery life. Perhaps for those whose mouse gets laggy over time, they are getting the lens for the laser dirty by tracking on dirty surfaces. I had that happen once with my 4 year old getting a hold of my mouse, but I cleaned the lens with alcohol and a cotton swab, and it began performing like new again. That goes with any mouse, though, not just this one.