I don't game much anymore, but using a gaming mouse in my day-to-day workflow is huge. Besides the normal browser history-back/fwd, I have buttons for scrolling through tabs, closing/reopening tabs, alt-tabbing between windows, changing volume, etc. I don't make much use of macros or anything, but if I worked in CAD or Photoshop I'm sure I would. I think any kind of workflow that's hotkey or shortcut heavy could benefit.