MaxMenus lets you assign a keystroke, like a function key, to cause a custom menu to appear. USB Overdrive lets you assign a keystroke to all those extra mouse buttons on things like the MS Intellimouse. If you tell USB Overdrive to "type" the same keystroke that you have assigned to a MaxMenu, what you have is a custom popup menu that appears directly under your cursor when you click the appropriate mouse button!
I use this in two ways: The middle button (wheel) gives me a popup list of running applications; this is a nearly instantaneous way to switch into another running application. Furthermore, if you hold down command-option this autohides all the other applications when you switch. Second, I have button four assigned to show all all mounted volumes; this gives you a complete file browser that appears at the click of a button.
Theoretically, this can give an amazing amount of flexibility, since USB Overdrive can be configured to map different keystrokes to mouse buttons depending on which application you are in. This gives the bewildering prospect of custom popup menus that are application specific. I haven't thought of a use for that yet, but would be interested to hear if others do.
[Editor's note: Cool trick ... I may have to download and register USB Overdrive!]

