How to find shortcuts?

I have a general question here, and a question about a specific instance of it also.

If you know the name or part of the name associated with a keyboard/mouse shortcut, it is easy to find it listed under the Input tab in the User Preferences window. You just type that name or part name into the search box at the top right under that tab. But, what if you have some shortcut and have no idea what it does and no idea what name or part of a name is associated with it, and you wish to find it listed under that Input tab? Anybody have any idea how to do that? Of course, I could just press the shortcut and see if I can figure out what happened, but that approach is really bad, I think. And, it is not at all fun to try to scroll carefully through every single entry looking for the shortcut I have.

That’s my general question, but it came to me when I tried to find a particular shortcut. In mesh edit mode, one can press ‘E’ to start an extrude of a selected face (or more). If you click the middle mouse button just after the ‘E’, then the extruding is freed from remaining orthogonal to the face being extruded. I can’t find the shortcut E,MMB, or anything like that, listed anywhere under the Input tab. Does anybody know the name of this resulting “free” extrude? I tried searching for “Extrude”, but no luck.

Here’s a complete list (I guess) for all the shortcuts in blender 2.5.
Some of them may have changed because I know this list since the first blender 2.5 alpha versions.

About the middle mouse button : actually this “shortcut” doesn’t depend on the extrude tool (E), you can use it with several tools on some different modes.
For exemple when you press G for grab on object mode if you start to move your mouse and clic on MMB the translation will be blocked along the nearest axe then if you clic MMB again, the translation will be unblocked (idem with scaling …etc).
This’s the same thing with extrude but with extrude the blocking along the normals is activated by default so when you clic MMB, you unblock the extrusion.
I do not see MMB as a real shortcut, it is more a part of several tools.

Thanks, sliv, that helps a lot. I understand and agree with your explanation for why MMB is not really a shortcut per se. Nice and helpful list also; good to have.