Blazing Speed is very useful in PvP, but requires a heavy commitment to fire that will likely cause you to use Scorch as your main damage spell. As we well know, though, Scorch is quite powerful in PvP due to its low cast time, relatively high damage for time spent, and ability to cause impact to proc. I am currently using a 34/27 hybrid spec in which the last two points in fire go to Blazing Speed. I find that the ability is nearly useless in PvE, average in Arena, and amazing in Battlegrounds. It is only average in Arena because you will likely not see it proc in needed situations due to the lower number of opponents targeting you. In battlegrounds, however, it seems that players tend to target you in mass, which will cause it to proc nearly every time you are focused. If you respond quickly, you should be able to flee the battle in time to save yourself, though not as effectively as if you would use Ice Block. The advantage of fire imo, though, is that it is easier to top the damage and kill charts in bgs than with frost if you can survive. It's just that fire mages normally don't live long enough to notice the results.