I came across a post on WoW Insider about the stresses of healing. As I read through the comments from disgruntled healers, a universal complaint seems to be that tanks and dps can't stay out of the shit (fire, void zone, breath, etc.)
I know this is one of my biggest peeves as a healer. Knowing what's going on around you is just something that every group or raid member should be doing. And there's not really an excuse not to pay attention and reposition. Tanks should have no problem maintaining aggro anymore, and while repositioning does negatively affect dps, it does so to a lesser degree than DYING.
No matter what your class/role, do everyone a favor and download GTFO.
When you're in the middle of a boss fight and everything is going crazy, it's tough to tell sometimes what is going on. GTFO will give you a loud, obnoxious warning to move when you're in the shit. Not standing where you shouldn't be standing will make the healers' job easier and raid survivability higher (since healers can concentrate on healing the damage that can't be avoided).