If slow actually had a purpose I'd agree with you Tyler. I played a shm on live to be the main slower. But here, there is never a reason to cast a slow. None. Mobs that can be slowed, can also be stunned. Stunned mobs do no dmg for the 5-9secs they are stunned and classes like the enchanter can chain stun.
I can't think of a boss outside the 30-55 zones that can be slowed. Everything is immune to changes in speed. It would be great if you guys could allow slows on bosses. Heck, scale the slows like on live, where even if you use a 75 percent slow a mob can only be slowed to 17-25 percent. But don't over do it like now, save the slow caps for the bigger bosses in a given zone or mix and match the mobs so one might be stunable and another slowable.