Hrm, not sure if this will apply or not, but since I run my druid/druid/priest team, I thought I'd chip in. I plan to use this all of the time... the only time I can see this NOT working is if you're using default action bars and have a warrior, paladin, or shaman in your team. I use HealBot, so I already determined that if I add any of those 3 classes (probably my pally) to the team at 80, I'll just move their stance bar out of the way. So, without further ado, here's what I do (yes, it rhymes, no I didn't mean it to lol)
I use Bartender4 for my custom action bars. Bar 1 is on bottom, then stacking up is Bar 2-4, Stance Bar, then Pet Bar. Because Bartender4 is an addon, I can move my bars anywhere I want them, so that I'll never have conflicting stances/aura's with a mixed team. I have a repeater region over my hotbars, that covers Bar 2, 3, 3, and my Stance Bar. When I want the druids to shift to tree/owl I just mouse over and click, or the same for flight form.
Now, because I have a class that cannot instant go to flying, I actually have a hotkey set up for mounting via GoGoMount addon mapped through ISBoxer. Using GoGoMount, I set my mount key to Number pad 1 key (Num 1) and my MouseButton4 (Logitech 5 button gaming mouse) so in ISBoxer:
Key Maps
> General
> Mount
Hotkey G18 (everything else default on the main page)
> Step 1: Target = All w/ Current | Key combination = Num 1
So when I want everyone to mount up, I just hit my G18 key (can make this anything you want, naturally) and they all mount. If I want to leave the priest behind and do something with just the druids real quick (useful for my cooking daily etc) I just mouse over flight form in the stance bar, click it and the druids mount and fly off. I like to keep things simple.
