toe-in or toe-out on the main gear ?   or none at all?

The only one I can tell you for sure is the Corsair, which has none.  Toe in doesn't help much when you have the torque from a 13 foot prop driven by a 2000hp engine trying to push you off the runway or a carrier deck.  There isn't enough of a contact patch on the tires to make much of a difference.  On multi engine airplanes, it easier to maintain direction with either light brake applications of differential engine power.

I would think that any sort of toe in would aggravate the tendency to ground loop should the pilot be careless enough to get into that situation.  I would also think that on aircraft with narrow track landing gear (Me-109 or Spitfire) that the ground loop tendency would be a lot worse if the gear wasn't straight fore and aft.

Good question, though.  Now I have to go do some digging....this might help, though it relates to model airplanes:

http://www.djaerotech.com/dj_askjd/dj_questions/staggerbee.html

thanks.....couple of things that I didn't consider there.......

   I like my toes in when I fly.