Not much. I treat BH like FH. When someone else and I Need Heals Now(tm) I use BH. Of course, holy has a bit more play with the spell since it is fairly efficient AND can give a serendipity stack.
I use it some but not often. The only fight it gets heavy use on is Chimaeron due to the caustic slime mechanic. Outside of that, I may use it like 10-15 times in a fight at most.
Use it quite a lot on fights where I'm taking damage - if both targets use the full heal it's about as efficient as Heal making it pretty awesome for the cast time.
I use it a ton. It's efficient, fast and it stacks up serendipity. When I am alone with my tank on Nezir it's probably my main spell. It can be situational but keeping yourself up is extremely important as a dead healer does nothing and BH is the best tool to heal yourself up most of the time.
It's awesome during Nefarian, when I'm healing the Onyxia tank. I only have myself and the tank to care about, and a spell that heals both is perfect for the job.
IF this applies to you, DO IT:
State of Mind was a viable Holy talent before 4.0.6 because I could get a jump on refreshing my Chakra or switch quickly if I picked the wrong one. It's now useless. Take those points and put them elsewhere. For me, I hadn't put much stock in Serendipity before, but I decided to after 4.0.6, since I had two talent points to spare... What a difference!
Going to what OP said, binding heal will trigger it, so if you and tank are both taking damage, its BH, BH, then cast your GH at FH speed!
What makes this talent even better is it procs off Surge of Light uses. In short, binding heal is VERY situational, but amazing when used properly.
as an above poster said, it's pretty damn sweet for Nezir tank healing (especially since it's always just you and tank, as you will jump to Anshal's platform with just tank during ultimate abilities phase)
I feel dumb for underestimating both binding heal and Serendipity before. They will make you a better healer. Count on it.