I was really annoyed with my Revolution when I first got it. My previous mouse was an MX1000 which had far more convenient buttons. I particularly missed the one between the forward and back buttons and the ones right above and below the wheel. These are very close to where my fingers are normally, so easy to use.
In contrast the Revolution has that weird dial thing on the side that you have to move your thumb away from the forward and back buttons to use. Then to replace the two buttons above and below the wheel it has a single button below the wheel, but so far back you have to contort your finger to use it.
Also it didn't let me map middle click to pushing the wheel sideways or something like that. Both the Revolution and the MX1000 make middle click way too insensitive, so I usually use clicking wheel sideways for that instead. For the Revolution I had to download a hacked version of SetPoint to pull that off.
It's also smaller, so my hand can't rest on it as easily.
Actually, after typing all that, I think I'm going to go buy a new MX1000.