Scott,
I'll back up Sven on this, I have one of those square-ish GE plugs around here someplace from quite a while ago... (If I remember right, I bought it for a late night repair from a grocery store) The U-ground pin broke off pretty easily simply from trying to pull the plug out of a paint-caked outlet! [Linked Image]
Look where the person's thumb is, there's one of the screws holding the clamshell body together.

-Randy