Had this another thread, but it's probably more applicable here.
Just to point out what an awful rebounder Okafor is:
He's averaging 3.5 RPG in 20 MPG. Over his last 5 games, you know now that the rust is off, he's averaged 2.8 RPG in 21.MPG. He has grabbed 14 rebounds over his last 106 minutes. For comparison, "small" 2 guard Avery Bradley is averaging 8.1 RPG in 35.7 MPG.
So he doesn't just suck at defense...