The tier 14 raiding system is a new experiment by Blizzard. I actually see Mists' first batch of raid content as three sub-tiers underneath the tier 14 umbrella. Mogu'shan Vaults is the introductory raid that can be done in mostly blue gear. The Heart of Fear requires purple-equipped raiders and a skilled roster. Finally, the upcoming Terrace of Endless Spring will be a challenge even on normal difficulty. The early heroic bosses have already been toppled, while I expect it will be weeks before we see the difficult Terrace cleared on heroic.
Everybody has to start somewhere, and chances are that you're starting in Mogu'shan Vaults. If you're equipped with a mix of heroic blues and an epic item here or there, you'll be fine in MV. Rogues are performing quite well in MV, in spite of being a melee class. We have several tricks that allow us to maximize our damage against the first six bosses that we face in Pandaria.