I've been on raids starting at level 46, and never had a problem with FD sticking, even at level 46 against 51+ Group x4 mobs.
But you have to really be careful not to have anyone in the raid train that mob near you, because it can and will almost everytime use an aoe attack against the guy training you, getting you killed in the process.
It's pretty cool having that spell in combination to my rez spell, because it makes me seriously wanted in raids. My guild is getting really good about not bringing the mobs anywhere near me while I'm FD'd, they've all learned to just move away and die. If at all possible, I find it best to try to get to the zone entrance to drop, that way the rest of the raid knows not to run there themselves.