This is my first effort to contribute as i have gathered some experience in Healing. I respecced resto a few weeks ago. The addon Healbot has been very useful ever since.
For those that haven't got it, you may download it from wow.curse.com. My post is mostly for a method i use to heal with the best possible reaction.
Most of the times, a healer is assigned to a specific tank/player and has the option to help healing other players, only if things get nasty. If there is a 5-man group though, or the healer is supposed to take care of many players in general, here's what i do:
I use both keyboard and mouse for casting. While i have my main target targeted and use my key bindings for those heals, i use my mouse to click the other player icons that Healbot window is showing. With this method, I only worry for the global cooldown, or any silence/interrupt that occures.
If my main target is a hostile mob, then I'm able to heal with the mouse and use the keyboard to shock/interrupt (shammy here) the mob as well, without the delay to switch targets, however little delay that might be.
Regardless, of this being known to some of you, i really hope that this will help those that didn't know it and make them better healers.