I'm a raid leader (or one of them) in my guild. I run a DPS/everything else you can think of meter called Recount (currently unsynced, but with a 200 yard range it generally doesn't matter). The important thing about Damage Meters is that they are interpreted based on the fight and the players.
The big thing for me is it shows who's using what skills and how often. I can then bug the healers about using their 1.5-sec heals as their primary heal, I can yell at the locks when they have any Curse damage up when they were on CoS/CoE duty, and I can compare skills used with DPS with gear to see what appears to be better. We've got a mage that uses almost only Fireball - nothing else. only about 5% of his damage comes from anything but Fireball. He's almost always the top mage on the damage meters. To me, that means he's one of the best geared, but also means his damage is slightly inflated because the other mages are the ones keeping up Imp Scorch. Our best healer was running massive overhealing on Gruuls - but, to put it in context, he was pre-casting Gheal while most of the others were casting reactively, or spot-healing, and he still topped the healing charts (which don't count overhealng). There was another shadow priest in the raid who, using that data, I can approach and make suggestions about her casting rotation and such, since I noticed there was a wide margin between us.
It's got other uses as well. You can compare were people "should" be - someone dies early (provided it's not from overaggroing), you can compare their DPS with others that have similar DPS and figure out about where they'd be. In Gruul's, ideally the only two people taking more damage than me should be the tanks - because if I'm doing my job, I'm popping SW:Death every time it's up. I can check to see who's throwing me the most heals when I don't need them, to tell them that unless I drop really fast and really suddenly I can heal it up with VE (more of a problem for me in Kara atm). I can brag about having 95% overhealing.
You can also see noticeable differences in some fights. Take Prince compared to Nightbane compared to Gruul's - on Prince, the mages and locks are usually quite a ways ahead of me; on Nightbane we're all fighting for #1; on Gruul's, I was #2 with a relatively large margin between me and the mages. Translation? On Prince, I have to interrupt my casting in order to get out of Shadow Nova range; in Gruul's, my DoT's are still ticking during the Silence and Ground Slam/Shatter. On Nightbane, we're all doing the same thing, so it comes down to spec, gear, and skill, and is probably the best of the three to determine who does "the most" damage.
Short version: It's all about context and correct interpretation. Damage meters become *MUCH* more useful in raids, on boss fights, than anywhere else, however.
Plus, it's still fun for me to just run BM and top both damage and healing :D
Edited, Jul 24th 2007 3:21pm by lsfreak