With the advent of the LFD tool, a lot of tanks are tanking PuGs at an unprecedented rate (as opposed to safe guild-runs). The problem with these groups is that they're often filled with exceptionally well-geared DPS that you don't know and that are only interested in getting through the dungeons as quickly as possible.
What this often leads to is serious aggro issues that have you alternately questioning your skill/value as a tank and cursing the stupidity of dps who insist on opening up full throttle on the entire pack the moment you've pulled with Faerie Fire on one. (I would like to note here that I am one of those stupid DPS, both in Cat and when playing Enhancement on my Shaman. I blame the fact that I spend most of my time actively trying to be top threat.)
If your group is full of AoE classes, there's not much you can do about this. I would suggest throwing your Faerie Fire while in mid-Charge and then start Swiping and Mauling for all you're worth.
However, if you have some targeted DPS classes in your group, there's more you can do to help. As you're getting ready to pull the group of mobs, throw a mark (usually Skull) on the primary kill target. You don't have to mark the whole pack. Just that first target. Just mark, FF, Charge, and tank. Usually by the time it goes down you have enough threat on the rest of the group that DPS can do whatever they want. With the 3.3 change that allows anybody in a dungeon group (as opposed to just the leader) throw marks on targets, it's even easier. Even though most groups will throw lead to the tank, even if you don't get it you can still mark.
DPS should have a /assist <tank> macro, true. But most don't, and not all that do use it. Plus sometimes the tank will switch targets for whatever reason and they may not want you attacking their target right at that moment, so it's slightly unreliable. But most DPS--from the fresh first-time 80s right up to the prima donnas--will kill a single marked target before going on to do their own thing.
In the image in this post you can see one of the Addons I use called LuckyCharms2. (Yes, I know it's been updated...I pulled that out of a Naxx-era screenshot.) It allows you to put raid marks on your target without trying to navigate menus or filling your action bars with macros. If you don't have it, or something like it, I suggest you check it out. Even when chain pulling through Heroics, this addon gives me ample opportunity to mark a primary target while running from group to group.
Hell, even if you're in a group and you're not the tank, you can help out this way. If you see that the tank isn't tossing out marks, use your /assist macro (you have one, right?) as they're moving to the next group of mobs, mark that target, and then do whatever it is that you do best. Some tanks may ask you to stop, true. If they do, let them tank their way and deal with aggro however they want to. A lot of times, though, you'll find that they'll start respecting your marks, too. :-)