Definite fold preflop and the rest of the hand is a perfect example why. Even if you hit your 3rd 4 there things like what happened on the turn can happen. I prefer hands like JT98 (4 cards in a row, preferably double-suited - though your flush still might be behind it still gives you a chance to redraw if you have a made straight with a flush draw on board). The only pair hands I really play are Ts and up, and the other two cards should be close to the paired one (ie. TJJQ or something like that).
This article seems decent:
The Ranking of Starting Hands in Omaha Holdem Poker. Part I | Omaha Poker Set
Also, check the one on this site:
http://www.pokerforum.ca/f52/plo-strategy-14869/