I wound up randomly grouping with a lot of people, some who I already knew, some who were strangers, and "pseudo-grouping" with a bunch of hordies (mostly hunters, though a couple of casters and melee). All of the hunters, regardless of faction, turned growl off, used MD appropriately, (either to me directly, or to their pet who was on one of my targets), and were generally a pleasure to play with.
Hunters in dungeons sometimes needed a quick reminder about it, and I did run into a couple who didn't know how to disable it. <.< Growl isn't a huge deal, but I have had some mobs with a nasty cone attack whip around and breathe on clothies due to a hunter pet getting a little out of hand, so I usually ask them to stop. I'm not particularly worried about the pet having threat for a couple seconds until I can smack their target, they occasionally get smooshed, but when they mess up positioning like that it's annoying. My "pet" peeve is spiders, actually. The webs are really annoying when I'm trying to round up a lot of adds, and they *don't* take aggro, so I have to go back and deal with casters who I'd carefully controlled on pull. :(