My first MX518 died after 2 years and even though i was somewhat annoyed by the short lifespan (my previous mouse, also from logitech, lasted 6 years if not longer) i bought a new MX518.
Should this one die an sudden and early death like the last one i will probably look for something else, i really like the Microsoft Sidewinder X8 play and charge feature, basically eliminating the only reason i don't buy a wireless mouse for gaming.
I also have the Microsoft Explorer mouse, which is basically the non-gaming version of the Sidewinder X8, i use it to control my HTPC (since doing it with the Logitech Harmony One really sucks) and the only drawback* of that mouse is the battery life, probably due to the silly feature that each time the mouse wakes up from sleep if illuminates itself with a bright blue light (not the BlueTrack light) and wastes loads of energy.
Edit: * i guess its large shape would also be pretty bad for gaming, but its quite useful and effective for use on irregular surfaces such as my couch or my leg.