if I feel a FH is appropriate and I'm missing hp myself, I BH
if I feel a FH is appropriate and I'm at 100%, I FH
I'm sure it's not uncommon for significant portions of my BH to be OH - but I don't run oom and I do try to be smart about it.
I know our holy priest and I definitely use both spells when appropriate and have learned to be less stingy as our gearscore/stats improved.