I usually get 2-3 per run and always wondered why. Then one day a MNK admitted I was getting commended because I DPS'd between healing. I told her it's normally a standard thing as long as the tank knows what he's doing and not dropping HP like it's a microphone. According to the MNK, she only gets a healer who DPSs 1 in every 5-6 runs on average, so it's pretty rare as of 3.0 launch.

It's nice being a healer though, as you are probably the only one in a party who can really study all the other members to see who is pulling his or her own weight. It puts you at a unique position. Because of this, I do end up commending DPS who I see using proper rotations and avoiding damage. I don't merely give it to the tank just for existing. Peeps have to prove themselves to get my vote of confidence.