I rolled a priest back in 2005 and the 1st 4 years Evlyxx was primarily a Holy priest. Shadow was my occasional "off-spec" and Discipline was this nasty kind of PVP spec that never appealed as it was neither healing nor DPS. It filled this strange place.
I knew a few priests that dabbled and then returned Holy and that was how it went. Then along came Wrath, Discipline was the revised and became a viable healing alternative spec. I stayed Holy, I liked Holy, Holy was priest healing spec. Then Blizzard did something that tempted me to try Discpline, they gave us dual specs, sure I could have gone shadow but there was this new thing I could test in raids and still heal.
My first few attempts I changed very little in my play style, casting renews and flash heals and just mixed in Penance on cooldown. Then as I became more comfortable I started spamming Power Word: Shield in 5 man heroics and noticed that if I did this the only person I had to heal was one with aggro, which meant the tank. DPS took so little damage the Power Word: Shield lasted its 30 second duration. Healing this way was easy. Then came ICC my raid healing now became spamming Power Word: Shield on everyone all the time. It was effective, in fact so effective that the only person out healing me was a pally who was healing the MT and OT with vastly superior gear. The only trouble was this was boring, pretty much how I got in The Burning Crusade when all I had to do in Karazhan was keep renews up on everyone and spam the Circle of Healing button on cooldown. I was not alone, all Disc priests ended up doing this as it was the most efficient way to "heal".
The developers at Blizzard realised this was not particularly fun but did want to keep Discipline as a damage mitigation healer. They messed with the spec and made some very nice changes. They made the Discipline mastery buff our bubbles, Power Word: Shield and Divine Aegis. During the first few weeks of Cataclysm Discpline was in a good place, my only grumble was that my Power Word: Shield was only as strong as it had been in ICC but this was the case for all of my heals so it was nothing major. Sure we lacked the pure healing power of our Holy buddies but while they were topping the meters spamming heals I was close behind and out DPSing tanks in 5 man heroics and 10 man raids meaning my contribution overall was greater and I was having fun using all the abilities in the priestly arsenal.
Then along came the big buff of 4.0.6, my bubbles were back, while I and the rest of the Discipline priests wanted to resist the urge to spam bubbles more frequently, there was the small matter that they had once more become over powered. Blizzard however were watching us and this past week nerfed our bubbles in 1 of the 3 ways they had available to them. They did this by increasing the cost of the bubble rather than reduce its effectiveness or slap on a cooldown.
I have only raided once since this change and it may be a tad early to make judgement but so far they seem to have made it really expensive so much so that more than 2 per rapture cooldown is causing me to be fighting mana all the time. Maybe I am doing it wrong I don't know but one thing for sure is that the days of Power Word: Shield and the bubble spam seem to be very limited and a disc priest as a raid healer just does not work right now. For me this is a weird design choice, the Disc mastery is bigger better bubbles but using them is really not an option unless you're tank healing which really puts us in a niche role or having a completely worthless mastery. I really am torn and will keep playing with both healing specs until I can get my head around the issue(s).
Seems my off-spec will remain Holy for a few weeks and my plan of grinding out Baradin Wardens rep as Shadow is on hold until I decide if my guild and I can live with Discipline as my healing spec or if I need to be Holy which right now seems the better all-round raid or tank healing spec.