Rotation and Scale have suddenly stopped working?

Question

I was working quickly, (making mistakes), and suddenly rotation and scale transforms stopped working. I think I hit some shortcut or button by accident. Translate still works though. I checked that the transforms weren't locked and such, to no avail. What could be the cause?

Answer 1

The cause is the manipulate object centers only button (Alt,):

When it is selected, scale and rotate no longer function normally.

Instead, of or rotating the mesh with the object origin, only the origin moves: