One of the biggest gripes that potential Spirit Masters had with their class was the inability of their pets to fly. It was a legitimate gripe, as their pets were a substantial portion of their DPS and utility. PvP in the air was tough for them for this reason and many a potential Spirit Master abandoned the class when they found that their pet was gimped in aerial combat.
In the newest Korean patch notes (translated version here) all Spirit Master pets have gained the ability to fly. This is fantastic news for everyone who wanted to roll a SM. It is also an excellent sign that NCSoft is listening pretty closely to the community.
Here is a short video of the pets in action: