[Big-Foot]

Okay - here's the skinny on measuring crank pins.

First off the journals you are concerned about are the Rod Journals.

Draw an imaginary line through the centerline of the crankshaft and the centerline of the crank pin. Orient that line so it points straight up (12 O'Clock).
With your micrometer, you will be measuring the crank pin from the 6/12 position and the 3/9 position (as though you were looking at a clock). You will take 2 measurements (minimum) starting from the front of the crank pin's bearing surface to the back of the bearing surface for each rod bearing. Mind you there are two bearings per journal (pin) in V6 / V8 engines.
You are looking for out of round, which comes from Detonation mostly - and taper, which comes from a bent connecting rod or bad piston.

Tolerances will vary from one manufacturer to another. I typically will call it quits on a journal if it is more than .00025" out of round or taper. If it's tapered more than that, make darned sure you have the rod's checked out or replaced. You cannot straighten a bent rod.

Contrary to the beliefs of many, you can turn a crankshaft as much as .060" without causing weakness in the crank that would ever be of concern in a street engine. You are, however, running a lot of material in the bearing and that could cause some degree of excess wear in a higher compression engine. I typically stop turning a crank when it hits .040" just because of the thickness of the bearings.

Hope this helps!