Yahoo! First team @ 80!

[Zappy]

For 5 man heroics, 535 defense = crit immune

[Ughmahedhurtz]

For 5 man heroics, 535 defense = crit immune

To expand, the rule of thumb is 5 points of defense per mob level. So it's 535 for level 82 mobs, 540 for 83 (raid bosses) , etc.

Also, for your ret pallies, don't sweat getting +hit gear too much. By the time you're in a few pieces of badge gear your hit will be plenty high enough. You'll quickly get to the point of wondering where the HELL all the non +hit gear is. :P