I'm so accustomed from windows for using the middle mouse button as a "close" button (best used for tabbed browsing, where the MMB opens a link you click on with it in a new window, and when clicking on the tab with the MMB it closes it... makes it very easy to quickly surf with tabs with one hand.)

Anyone know how it would be possible to change the behaviour of the MMB? The default Gnome/KDE options are not very extensive.