Caseback, crown o-ring, and if you're building it the crystal should be pressed in well. Make sure that the CG is pressing the crown in far enough to compress the o-ring.
I agree with parts of both sides here. My opinion: I trust the dealers I work with that if they say it's waterproofed, then it is. However, when I spend 2-300 on a watch, I refuse to rely solely on trust. That's why I take the 15 minutes and spend the $20 and make it an issue of experience instead of only an issue of trust. I understand that smas and others (myself included, way back when) have had verifiable experience of waterproof out of the box, but myself and others also refuse to leave it at that. That's why I also do my own regulating, cleaning, etc. out of the box in addition to waterproofing. I like to be sure, is all. I mean, trust in your dealer verified by pressure testing is surely better than trust alone.