What i am trying to say is, forget the 1/focal length rule, when using tripod, you can break it to the point the object(say a person) can't hold himself steady enough... is there a minimum shutter speed for this situations?
I remember trying to take a shoot with rear flash/tripod of my mom, because the shutter speed is automatically set to some really slow shutter value, it was hard to get a sharp pic... and yes, it was focus correctly, I think...
Even though the camera is on a tripod you can start with the same 1/focal length rule; since what you're minimizing is the relative motion between the camera and the subject. Usually we assume the subject is steady and the photographer is not; but this is just the reverse.
That's a tough question to answer, I don't take chances with moving subjects and opt for the highest shutter speed possible. The one that always catches me out is when I photograph a static subject outside on a windy day, the things that move in the frame that I overlook always look poorly focused.