Used the M60 yesterday for a detailed 6-8 hours and it was a good and comfy experience. Loved the side buttons (including the 'sniper' button). Buttons are all well placed and well within reach, easy to use.
I'm currently using it on the default dpi settings it came with and they need a little tweaking, which I haven't got around to doing yet. Loved the scroll wheel. The mouse click was a bit hard for the initial hour but then it was smooth. Just adjust the dpi settings as per your preference via the software (which you'll need to download from the website/ web).
Love the way my finger can sit comy on the wheel all the way down between the left and right mouse buttons. Makes clicking all the more easier as I don't need to lift my finger much for clicking them, especially over extended hours.
The glide is a little rough but that's because I'm using a sh***y CoolerMaster mouse pad which I've never been much happy with. So, the surface apart it's performing great
The sniper button is very well thought of and very useful. The button isn't hard to press and well within reach (I have big hands so no probs for me). I'm somewhat between a claw and palm grip., but haven't had any issues on that front with this mouse.
All in all, I'm very happy with it.