I believe the problem here is a bit different than most people think, though its hard to notice. I believe we got the "Reserving Instance" problems again, due to high volumes of instances created they max out available slots and people need to wait for a slot to open in order to make their "new" instance.

Yesterday i queued with tank and was waiting on a full group for 10 minutes for "reserving instance". I assume the problem is even bigger with Healers and DPS