Operating system and graphics card
win 7 64 bit, nvidia 760gtx
Broken: (example: 2.69.7 4b206af, see splash screen)
Short description of error
Minor flaw. The tooltip for the mirror tool in Object Mode says: " Mirror selected vertices around one or more axes " . The word 'vertices' is imho wrong here since you cannot select vertices in Object Mode. And there is geometry that has no vertices at all, but can be mirrored by the mirror tool too.
Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
Open Blender, stay in Object Mode, hover with the mouse over the Mirror button in the Tool Shelf. Have a look at the tooltip.
Possible solution: replace the word vertices by the word geometry. Then it fits to both modes again. And makes also more sense for geometry that has no vertices.