WowInsider posted another Boomkin guide last week.
http://wow.joystiq.com/2011/03/25/shift ... -rotation/

It's not specific to AoE, but pointing it out for the section on AoE specifically because it was definately the most useful bit of the article and it taught me a few things that I simply didn't know before; i.e. that you should avoid hurricane and go for Moonfire/Sunfire.
Basically you should put mushrooms down as a priority, but after that you should spam Moonfire on all of the mobs one-by-one (making sure to keep moving to keep the buff up).

I tried it on the AoE trash mobs in last night's 25-person raid, and for those specific pulls I was second on DPS (only Andro managed to beat me).
Obviously AoE is only about 10% of what we're usually called to do, so this isn't exactly worthy of waving an ePeen, but at least I'm starting to playing my class a little bit better.