In regards to your statement of never having to stop to clean the mouse here -
http://www.logitech.com/lang/pdf/wheel_mouse.pdf - I just experienced the contrary.
In recent months of using my mouse, I have been experiencing erratic behavior of the mouse, such as document scrolling "jitters" without actually turning the mouse wheel, intermittent shutting itself off, an incredibly difficult wheel button click, and mouse pointer jitters without even moving the mouse. These symptoms all happened no matter whether I had it connected via USB or PS/2 and no matter surface I placed the mouse on (ranging from unfinished wood, finished wood, to a generic plastic/rubber mousepad, to a white piece of paper, to a cloth/rubber mousepad, and even denim jeans)
Today, I cleaned the mouse and every single symptom I just listed ceased to happen.
Therefore, your statement of never having to stop to clean the mouse is false.