I'll second the comment about Logitech mouse drivers. Avoid them at all costs. They're just awful. Took me 2-3 hours and lots of reboots (reboots, on a Mac? Yep.) to get rid of them entirely. Kernel extensions, library files, etc. If you love Logitech mice (I do), or any other fancy multi-button mouse, buy a copy of USB Overdrive to completely replace your mouse drivers. You can assign any function to any button, per application or globally.