I use object_origin_set a lot, that's assigned to shortcut Shift + Ctrl+Alt + C , and since it's a 4 keys shortcut, I searched the object mode shortcuts on Blender Wiki and in the user settings, I found that Ctrl + Alt + C is not assigned, so I thought, well why don't I lose that extra Shift that causes my ring finger to stretch to un normal limits every time. Well it doesn't work, I tried Ctrl+Alt+A it worked, I'm curious, does anyone knows why is this specific shortcut not working?
⎈ Ctrl⎇ AltC isn't working as another shortcut is assigned to it and is used before the set origin shortcut - it will clear constraints, so you probably didn't notice anything happening.
If you untick the Clear Object Constraints shortcut you will be able to use ⎈ Ctrl⎇ AltC.
As shown above there are several groups that a shortcut may belong to, blender goes through each group and uses the first match found. Fairly sure the search order is the same as what is displayed in the input preferences. You can have some duplication as some groups will not match the current context, for example the clear Pose Constraints shortcut will not match unless you are posing an armature.