Originally Posted by
angrylol
There are plenty of addons, like Omen and a bunch that shows threat on nameplates.
There is also a built-in system that colors your target to red(secure) to orage-yellow-ish when there is someone approaching your threat. You can even enable it to show % iirc.
Frost presence gives you threat multiplier in general as well as some high treat abilities - icy touch, death and decay and rune strike. And losing aggro is not an option on most bosses in raids(cones, cleaves, etc). Usually it's not a big deal, but it end in a wipe somtimes. Either way, it's a clear sign that you are not doing your job.