I bought this keyboard as part of a desktop set in 2010 and it worked perfectly, straight out of the box.
I noticed the difference immediately as my wrists were no longer sore when working and the keys were very responsive. I love the media keys on the keyboard as it's so much easier just to press a key on the keyboard than to keep using the mouse.
After about 10 months, some of the letters started to rub off on the keyboard, which is not a problem for me as I am a touch typist and use the keyboard for about 6/7 hours a day. A little while after that, I noticed that some of the keys weren't as responsive as they have been, esp. the keys under the little finger, i.e. a, p, q, etc. I initially thought it was my fingers that weren't strong enough until someone else who has the same keyboard pointed out that these keys were quite stiff. I think if I were not a touch typist and press very lightly on the keys, I would not have noticed this at all.
I contacted Logitech who replaced both keyboard and mouse within a week of me contacting them, so customer service gets 5 stars from me.
I would have given it 5 stars, but for the fact that I had to have it replaced after only 16 months but 5 stars for the 3 year warranty as well.