absolutely brilliant
Basically my 6-7 month old MX518 was suffering from internal issues, most likely the USB cord or wiring (random cut outs, dropping down to 800dpi etc...)
Contacted Logitech on 9th Friday, swapped a few emails over the weekend, Logitech granted me a replacement which shipped yesterday (Tues 13th) and it is now with me TODAY.
Next day from Germany, brilliant.
ps there seems to be yet a new version of the mouse circulating
still 1800dpi but the underneath is completely different
(not my pic)
http://img296.imageshack.us/img296/6788/dsc01532eo3.jpg
Movement is much more slippery, I use a cloth based pad for generally more friction, however it now moves like its on an Icemat :S