Spellpower of Malfurion posted on the Priest forums that spell pushback is an indication that Blizzard prefers melee classes over spell casters. In his thread, the original poster used the example of a sixteen-second actual cast time for a second and a half spell due to spell pushback. This greatly reduced the effect of casters against melee classes. Songbreeze of Dragonmaw echoed this sentiment with the response, "Welcome to World of Meleecraft."
Other posters disagreed. Some stated that many PvE encounters favor casters. Nemarra of Tichondrius pointed out that melee characters have an equal disadvantage at range. Casters also have access to instant spells and abilities such as Blink, Frost Nova and Curse of Exhaustion to help them get out of melee range. Others have access to Power Word Shield and Earth Shield that mitigate the effects of pushback. If you're concerned about spell pushback, you should pay particular attention to how your spec can mitigate it.