In the vein of that other thread saying you can continue BG achievements by logging out and logging back in only after the BG ends, I found out today during a naxx run that statistics done outside BGs count toward BG achievements as well. Observe...
http://img6.imageshack.us/img6/8818/...1009154659.jpg
Check the chatlog. I'm going to do testing later to see if this works with harder ones like wrecking ball and BG specific ones, soon as this naxx ends. The player confirmed on vent that he had logged out mid-BG earlier in the day and hadn't rejoined one. At the very least it could be useful for Damage Control
(the shaman in question who got the achieve was ele, got the achievement from healing stream ticks, this was the second wing in)
and inb4 people try to give me shit for not blacking out names, who cares?