I normall check the Emulate 3-Button Mouse box. This feature is used with a two button mouse by clicking the left and right buttons simultaneously (at the same time), so it is interpreted as a middle mouse button. This is very handy for quick pasting, where I click and hold the left mouse button and drag it over text to highlight it, then move the mouse to anothe window (dialog) where I click the middle button to paste the highlighted text. I miss this feature when I am not on Linux and want to cut and paste.
