A 12x12' shed, in the shadow of a 2-story house and surrounded by trees? Seems as though the 12/2 feeder feeding a 2-circuit panel with two 15A circuits aught to be plenty with just the #12 Cu ground.
I do have a problem with this related to several real sites, too. In commercial/industrial construction, we generally have a power vault on a corner of the building, often with switchgear, generators and UPS. What 250.32 says is that this is fine so long as that CMU wall is shared, but move that power room 5' further away to create a fire gap, and suddenly, I've got a real grounding problem with every single one of my subpanels.
Granted, I prefer to use multipoint grounds as much as possible, but there are some cases when a 250.50 ground connection is impractical, otherwise unnecessary and very expensive.
[This message has been edited by SteveFehr (edited 10-24-2006).]
