Raid exp used to be very low, and I think you don't get any at all anymore. I know that while leveling in BGs, I would often see a message like "NPC dies, you gain 25 experience (-25 raid penalty)." That said, MC can be cleared pretty fast by a group of 85s. I used to do it in under an hour with my shaman/4 hunters, and I never particularly rushed it. They nerfed the gold drop from bosses but it's still a decent haul for the time spent.