I use the forward/back buttons on my mouse to assist in navigation in windows all the time. It's extremely efficient to simply go back to a previous folder or forward to the one you just left by just clicking a button.
I would love to see similar functionality in the ArcMap environment applied to the extent history in data or layout view. So, when you click the 'back' button on the mouse, ArcMap gos to the previous extent. Similarly, if you click the 'forward' button ArcMap would go to the next extent.