I assume many raiding guilds are aware that cloth healers are on the short end of the stick when it comes to receiving healing loot. They will never roll on an item with +hit on it, that's dedicated for DPS of course. However DPS will roll on every other caster gear too, making the competition rather high. Currently I think holy priests are the ones who are lacking the most love. Some give mp5 loot to healers first, but that is currently not the stat you go for as a holy priest. However, lately I've gained some hope that mp5 will be a more crucial stat after the 3.1 patch. I am looking forward to see how the mana-regen-nerf will affect us in practice. Depending on the result, the mp5-gear might be the thing to go for and making holy priests get a bit of priority on loot.
I remember in the old days we often tried to gear up tanks and healers first, as they most often are the most crucial classes. An interesting mechanism is that once you reach a "good enough" gear level as a healer, you don't really need to bother to maximize the gear. It will hardly effect the raid at all. So one way to go when it comes to loot distribution could be to give healers priority early on when going for harder content, and then have DPS move up as the raid makes progress. I can't say I would like to manage such a system, but perhaps it is manageable to some extent?
I would be interesting to hear how others are dealing with this issue, if at all.