Personally I have used the DeathAdder for about 5 years now. I use one a home and one at work. I have only replaced one mouse in those 5 years and that is just because I had worn the majority of the rubberized coating off of the mouse.
Hmm. I had one a year or two back, and the thumb buttons got to the point where blowing on them would activate them - and that was within a few months.