If you've ever wanted a close-up look at the game's healing zeitgeist, Miss Medicina has it -- she recently started up a survey/meme of healers around the WoW blogosphere, and the answers are now in and posted on her site. They make for some interesting weekend reading, especially if you're interested in healing and what healers think of it. I'm sure there's lots of conclusions that could be drawn out of this (I'll let you all come up with some in the comments as well), but just reading through them on my own, it seems like there's a few threads between them. The majority of healing seems to be done in 10-mans, which probably isn't too surprising, given that's where most of the endgame players are right now as well. There's no clear winner on class or spec (all four healing classes are represented pretty evenly, though I didn't really crunch the numbers), though there are quite a few priests, and of those, things seem to be split between holy and disc.
In terms of a favorite spell, there's almost no crossover at all -- people are all over the place, from Beacon to Penance to Circle of Healing. To hear these guys tell it, healers have all kinds of fun spells to play with. In terms of a weakness to healing, two main answers appear: mana regeneration (always an issue with mana-heavy classes like healers) and mobility. Shamans and druids have problems with big burst healing, and paladins say they need more group healing strength, but almost everyone mentions either mana or movement. There's a lot more to look through, too, in terms of how healers evaluate their performance and addon recommendations from everyone. As a look inside the healer "scene," there is a ton of information in there about what healers are up to out on the realms.