I never used ProH in TBC, I rarely used it in Naxx and now I use it quite often in Ulduar, I think we've all matured to where we can plan groups depending on who will be where, even though (most) buffs are raid wide there is a benefit to placing certain members in a group, I enjoy having 4 of the other healers in my group during fights like Kologarn and Auriaya so that when the "predicted" burst happens I can get a good important heal on all the healers so they can worry about the raid first and not themselves.
ProH is an expensive spell, you can't spam it as others have said and I'd wonder why you would spam it without it stacked as a buff as the cast time is too long to be worth it. Typically my healing meter on recount will be CoH 27% ProM 23% ProM 19% with Flash Heal just behind. That's the usual order and percents are off the top of my head, but roughly accurate.