loving the Echo tie in with the plane!! very cool!!! although the black smoke thing was weird - so was it scared of him because he is a priest ??? - cos I got the feeling he actually DID become a priest after his brother died right!?!?!
I don't think "it" was scared of Eko. Remember back in S1 when Locke first sees the monster? He looks upon it with awe, not fear. He does not try to run away or attack it. As shown by the reflections in the smoke in this episode, "it" can access people's memories / read their emotions? Eko didn't seem to be scared of it, like Locke. So when it is approached with fear and hostility, it will retaliate, but when it is approached peacefully it will not attack.
Or I also read somewhere a theory that introduced the possibility of two "monsters", one peaceful and one malicious..