I just installed the 2x2 = 4GB ram from OWC. The first try, my macbook pro won't boot in to leopard and there's strange lines running through the screen. I switch the rams to different slots, and it works. Now I've been booting up and shutting down for about 5 times, and it still works perfectly. The only problem I have right now is that my machine seems to be slower with these 4GB OWC ram than it was with the stock rams. Do they need time to adjust or some sort of burn-in period? Anybody also has a lower performance with 4GB?