When a chess board is properly set up all four Knights should face each other. I.E. face on. After the Knights move, you can place them any way you wish.
Are you citing a reference on this or is this your thought on the matter?
The Knights are set up this way in World Championship pics I have seen.All four Knights were faceing each other across the board. Other than this I guess it really dosn't matter.
I guess you mean each knight faces the one of the opposite colour on the same file? It's kind of hard to envisage a knight facing more than one other in the starting position!
I always orientate them to the East! (it has a symbolical value, cf.: http://www.amazon.com/The-Journey-East-Hermann-Hesse/dp/1891396889)