So I am almost full time Disc, and I'm Aposematic's assigned raid healer, pretty much, since our other healer is a paladin. In PuG raids I also tend to do raid healing with the occasional Penance on the tank, and I've seen the same with other Disc priests.
Disc has the reputation of being the tank healing spec, and it makes sense in a way, but I feel really comfortable just bubbling everything in sight, throwing Penances and FHeals where needed and using Prayer of Mending on the tank and Renew on whoever needs it in the time I have spare. Okay, I use ProM a bit more than that, but you get the idea. And it works very well, plus I'm personally much more comfortable with this than with Holy.
The only place where it hasn't really worked out for me so far were Precious and Stinky but that's when I can speed up my Prayer of Healing with Berserking or Power Infusion and we still make it somehow.
The reason I make this thread is that I read this (I know, old) in my infinite boredom yesterday and feel that whoever is interested in priestly things should not have some silly prejudice against Disc. Because we're even more awesome than people usually think.