I have an 8-button Logitech MX500 optical mouse, and this week is the first time I've ever successfully mapped functionality to all the buttons. Windows did a reasonable job with a few of the buttons; Linux doesn't support anything beyond the first three; Mac OS X Server just gets it done.
Out of the box, my third button (scroll wheel) is mapped to the seemingly pointless Dashboard, which is a huge pain when you're used to middle-clicking to open a link in a new tab or to copy/paste text in a console. To get that functionality back, go to
Applications > System Preferences > Exposé & Spaces then remove Mouse Button 3 from the Dashboard's "Hide and Show" feature.
Next, I set Mouse buttons 5, 6, and 8 to All windows, Application windows, and Show Desktop.
But even cooler than these is Spaces,
though as yet I can't find a way to replicate Gnome or XFCE's ability to move windows from from Space to Space which lets you drag open app windows from Space to Space which in the Spaces view (F8). Still, having up to 16 virtual desktops is very handy, particularly when you need to virtualize Windows and Linux. If you want to be able to have console windows on all Spaces rather than having them all collected on a single Space, uncheck the "When switching to an application, switch to a space with open windows for the application".