Let me clear up Logitech free-spin scrolling: There are two versions of this technology. The first was introduced with the MX Revolution. The second was introduced later, like on my MX 1100. Here are the differences, and I'll try to be clear because they are subtle:
The scroll wheel has two-modes. It can scroll click-by-click like most mice, or it can scroll with a free-spin (think of lifting a bicycle off the ground and spinning the front wheel, that's exactly how it is). But how do you switch between the two modes? Well, one way is that the mouse detects it automatically depending on how quickly you flick the wheel. If you go really slowly, it will just click-click as usual. But if you give it a quick flick, it will go into free-spin mode. The other way is to set the wheel middle-button click to switch between the two modes. The disadvantage to that is that you lose the ability to program the middle-click for another function.
I think this information is correct, but since I don't own the Revolution i may be off. but I used it in stores.
The problem with the technology above was that, apparently, many users just wanted to be in one mode or the other. They didn't want the mouse to automatically determine which mode is best. maybe some users want to flick the wheel hard, but don't want to go to free-spin mode. So, Logitech changed the technology.
OK, this is the one I have (and love). On the MX 1100, the auto-recognize spin mode was taken away. If you want to switch modes, you simply press the little button located behind the scroll wheel. In the Revolution, this button was some kind of "quick search" button where you can highlight a word, press the button, and have the word automatically googled or something like that. Anyway, so that's it. The wheel is either completely in free-spin mode or in click mode. No more hybrid, auto-detect mode.
I love the free-spin mode and use it 99% of the time. The control you have with it is exceptional.
I hope that clears up the technology. i was confused for a while also. i had to read a lot and go to the stores to try them before I understood completely.
I also want to clear up another point of confusion. The Logitech free-spin mode is more than just not having the click. I used to have the Microsoft wireless mouse and it didn't have a click either...it was smooth. but it wasn't free-spin. There was a viscosity to it. Free spin is just like the bicycle example I mentioned above. Other mice may not click and be smooth, but they probably can't keep spinning with a flick.