I didn't truly "get into" Mass Exorcism until 5.2, at the behest of a friend. I was quite hesitant to sacrifice the ranged nature of Exorcism for some AoE damage, but she insisted that I glyph Mass Exo for a week and get used to it. Reluctantly I grabbed the glyph off the auction house and scribbled it into my spellbook. Three raid days later I was as pleased as could be at the boost to my DPS, but I think the larger change occurred in my cheapest wow accounts perspective.
One encounter for which I thought I needed an at-range Exo was Lei Shen. The tanks kite the boss from corner to corner, adds pop up in different quadrants during transitional phases, and winds push you every which way near the end of the fight -- all of these seemed to beg for more ranged abilities to be able to handle them. As it turns out, though, I was thinking of selling world of warcaraft accounts it the wrong way. Instead of seeing myself forced out of melee range, saying, "Well, if I have to be out here I should do as much DPS as I can until I can get back," what I really should have been thinking was, "How can I get back into melee range as quickly as possible?"
We are a melee class; as much as some of us want shockadins to be real and viable, the bulk of retribution's damage comes from hitting things really hard with a two-handed weapon. Therefore, instead of focusing on how to maximize DPS during those few moments when I was punted away from a boss, I should have been trying to find ways to minimize the time I spent away from the orbit of my foe.
Of course, encounters with only one target do not quite necessitate the use of Mass Exo, but I have found that unglyphing it only to get best wow gold avoid the cleave (on Primordius or Twin Consorts, for example) helps me focus on what's important.
I bring these points up not to taunt warriors or other ill-equipped classes and specs, but as a roundabout way of saying that I can sympathize. These abilities didn't exist before Mists, which to me shows that things can and will change. Exorcism hit like a wet noodle in Wrath, and there were many, many instances where using your Art of War proc to cast a Flash of Light instead would be a better use of your time. Look at Exorcism now: its damage is second only to Hammer of Wrath, and when glyphed it can be an amazing source of AoE DPS.