It's a special app you get from the Logitech site that is supposed to make the scrolling smoother in web browsers. Apparently it's not too good because it was also causing a slowdown in the shutdown procedure of Windows 7. I would always get a notice that it had to wait for background programs to close. Now it doesn't do that. I also have the Setpoint suite installed so I can set my scroll wheel to do a double click when it's pressed. Most Logitech mice will work without Setpoint if you only have a 3 button one.
I only have the $8 M100 mouse myself but I wanted the double click function so I installed the driver suite.
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Mine is a big beast, it needs setpoint as it is highly configurable. It is great ergonomically and has 8 buttons, all of which can be programmed to do many things. I have programmed three, two of then that I use my thumb to activate and boy does it make general browsing much easier.
It is the most I have ever paid for a mouse, at the time it was the top of the range Logitech one at the time, it cost an arm and a leg and wasn't the one I was looking for, but the next one up. I paid over the odds for it as I bought retail from a computer store as I wanted to see it in real life. Could have waited and ordered on-line for a cheaper price, but would have paid carriage then.
I broke my right wrist a few years ago and ever since using a mouse has been a pain if I over do it, this one is much better, so I guess I got what I paid for.
