While playing Fleck one day I thought, "These actions would be quicker and easier if I had a double-click button on my mouse." Until now I've been using the same Logitech Marble Mouse with two buttons for 5 or more years. I discover the current version contains four buttons. Score! I use my Logitech gift card (from the delayed release of the Logitech Revue with Google TV) and have an amazing mouse that I don't know how I lived without.
How did I survive this long with a two-button mouse? On top of the obvious benefits of a multi-button mouse, I am a gamer and therefore accustomed to multiple buttons. I use keyboard shortcuts all the time. Seems to make logical sense to have a multi-button mouse. Opening an e-mail is now one button. Opening a file is now one button. Now I need to find a purpose for the fourth button. For home I purchased an even crazier version of the Marble Mouse. It has a scroll wheel and seven buttons. So many choices!
What actions do you assign to your 3+ mouse buttons?