I reinstalled Recount after the Vengeance changes in patch 4.3 because I was curious about how much damage it was adding to 5-man tanking (answer: a lot), and then again to see the damage differential between PvE and high-end PvP gear. Afterwards, I just never got around to uninstalling it. If I'm more than 50% of the group's damage as a tank, it's generally best not to stress groups by asking if they want damage-dependent achievements, and a few pulls into Zul'Aman, I'll have a good idea of whether aggressive pulling for a bear run is likely to pay off. Spamming the meters doesn't help anyone, but if you're just using it to inform rather than dictate the play experience, then I'll admit it has its uses.
Do you use damage meters? Why? And what's the best use -- and the worst abuse -- of them that you've seen?