Getting across that DMZ is easier than putting your PS3 in one.
I had real issues with Bad Company trying to join games with by brother in law. No issues with any other game except that one. I ended up looking at a guide to put PS3 in a DMZ but gave up in the end.
I played the other night and had problems, not just join errors but the big crash bug. The crash bug is even stranger now as if you get a kill against the player who gets the bug you get a kill every time he explodes. I saw the message I killed someone 4 times in a row, and got the points for it. Pretty weird