At the time of writing this I hadn't done a ton of dungeons but I had ran into some instances of this and had literally just got out of an annoying group where a dps was just doing his own thing. I agree that, since I've had more time to play, this doesn't happen all that often. I guess I just hit a streak of runs where I had some eager beavers. It's actually been just fine lately, no issues really. I still don't think people should run ahead of the tank and do what they want though. At the very least communicate something beforehand. While I've never minded myself about the pace of a tank, I encourage those that do to simply speak up before just doing whatever. The tank can do the same and should if needed.