Great mouse while it works, but the plastic that contacts the click buttons wears out for some people and the clicking becomes much less responsive. Used mine for about a year before the problem surfaced; ended up having to take it apart and glue a piece of tin foil to the plastic under the shell so it makes contact with the button once again.
Do a google search for the issue and you'll see people complaining about it (happens most often when you try to hold a mouse button down). Logitech was even offering free repairs for people within certain time periods of purchase.
Again, besides that, the mouse is awesome.
I wouldn't be surprised if they were still doing repairs. Logitech's policies of device replacement and customer service are some of the best out there. I had a G7 mouse that I bought from Newegg 3 years ago, it finally stopped connecting to its receiver so I figured no big deal, we had a good run. Contacted Logitech anyways to see if there was anything else I could do to fix it, they immediately shipped me a brand new G700 (MSRP $100.00) on the spot. No questions asked, didn't even ask me to return the broken one. I've never seen anything like that before or since.