I bought me an MX700 today and so far it's worked great. I just finished programming the side buttons for Quake III. As soon as I try it out, I'll let you know how they work.
The main thing I like about it is it's heavier than the MS Intellimouse Optical I was using which I think will help with my aim in FPS games.
MAC
PS: I lucked out today by buying it. Best Buy had a $20.00 rebate going on for the MX700s that ended today.
EDIT: For some reason, the side buttons are not working in Quake 3. In the Logitech mouseware I set the side buttons as F8 and F9 and added the binds to my 3wave config, but they don't work. I'm gonna have to do some more investigation on this. Also, during one game last night, the Mouse 3 button quit working. I had to leave the server and restart Quake 3 to get it back working. Other than these small glitches, the MX700 is great!