I've used my MX518 for 6 years and it still works fine, only needing one cord replacement and new mouse feet.
The thumb area has worn out for me too, but that was about 4 years ago.
I second the recommendation for the G400, its the new version of the MX518 and just as reliable from what I've...
bump I have the same exact camera and lenses/adapter and can confirm that it is great, especially if you are interested in shooting video. it does 1080p60 and has the same sensor as the nikon d7100
love my mx518// bought mine in 2006
2 biggest qualms,
125hz polling rate (8ms input lag)
the feet are so small (older version), it really affects the glide, i also have a logitech g7 and the bigger feet glide way better