I have a Microsoft Wireless 5000 mouse, which I really like. It fits my hand well, the batteries last a long time, etc. However in addition to the two main buttons on the top, there are two side buttons near the upper edges. I rarely use them, and their defaults are magnify (right) and back (left).
Normally they don’t bother me, though I do tend to hit the magnify one more often than I’d like. However today I was editing something and hit the left one, moving my browser back and lost some work. After cursing the computer for a few minutes I did what I should have done a long time ago. I popped open the control panel and disabled the buttons.
I’m sure some people really use them, and it’s good if you can get used to having more functions on the mouse since you don’t have to move your hands as much. However it’s a hassle for me, so I’m glad I have the options to disable them.
Now I have a nice shaped mouse that fits my hand, has a good design, and doesn’t get in my way.