This is a big problem I have seen for a lot of other tanks, and a big part of it is where the tank positions himself within the enemies hitbox. So often I see tanks keeping a discrete distance from the boss which puts them in the wider part of the field when a breath happens. This means they have to run farther to get out of the area, and if the cast is too quick, they will never make it. I am a tank myself and our raid leader and I make sure to train all of our tanks that you don't need to stand 10ft from their nose so that it looks more like a fight. Tuck in on the smallest part of the hitbox in front of the enemies (which should be about 1ft in front of its pivot point) and when the cone shows up you only have to take 2 steps through the boss to miss the attack and 2 steps back to keep him from turning. I usually walk backwards because of how slow it is you can usually dart forward and then immediately start backpedaling. This way, the attack misses and the boss doesn't even budge because you are back in his face before he finishes the animation. To me, this is one of the MOST important tactics for a tank to use. For big AOEs of course things are different and you want to stand as far back from the enemy and still maintain range.
Not for breath attacks. Dragon attacks are rectangular and it doesn't matter how close you are on those. For all conal abilities? Absolutely, facehump that boss so you can move in time.
Casters are ridiculously easy to deal with as a tank: just run through them. So many have problems with the first boss in AK and take so much damage because they don't bother to dodge his Thunder III via running or interrupting.
EDIT: Brayflox's Longstop is the first instance where the difficulty ramps up (then decays again until around Stone Vigil), but also where those that have raided in other MMOS (especially WoW) have a distinct advantage.
I've been tanking for nearly 10 years across MMOs and when we fought the last boss in BL it was just like fighting old Grobbulus from Naxxramas: slowly move him around the edges of a room like a mutt and dodge the red lines. The mechanics are virtually the same. Edited, Sep 19th 2013 5:12pm by Viertel