Do you keep Lava Burst on your bars? Most PVPers aren't smart enough to check the actual spell being cast and will usually interrupt a healer at the first chance. Put Lava Burst on your bars and cast it instead of a heal if you see an interrupter on you. This way, you're only locking out your Fire tree, which is just Lava Burst, Fire Totems (I think those count) and Flame Shock. Draenei Shaman used to do this with Gift of the Naaru (Holy spell), but I don't think it has a cast time anymore.
I keep it on my bars and use it sometimes (that little bit of burst after wind shear to help kill the healer is awesome). Fake cast with a greater healing wave (having something with healing in it makes it just too tempting), combined with an interrupt tracker it does help some, sometimes. Just the other day I had 3 on me and I pulled the interrupt from all of them and had several free casts. Haha, that seldom works but when it does...
Then again, sometimes you fake cast, no int, fake cast, no int, fake ca... hey I'm dead. Then the times you hold it too long and they actually do catch ya.
So, as an aside to my above story Bliz found people weren't dying in BGs fast enough and did a -30% nerf to healing Tuesday.
EDIT: I miss banishing trees, but I've been killing them all right, surprisingly well on my lock. Post nerf I've solo'd several druids of various varieties, I think at least a couple restos. My opinion of OP in this transient environment would include mages (!!!) and holy pallys. I had a holy pally just destroy my nearly full Cat equip'd resto shaman, and mages are dominating the charts.