I played with a guy who played a solo boomkin in PVE and PVP. He could top teh DPS charts in any BG, AV was harder but he could do it. He could also top the charts in Kara if he was only DPSing, sometimes even when he would off heal. He was also one of the best pure gamers I have ever played with. He once tanked attumen and midnight in kara as boomkin. His gear was mostly T4, we didn't raid past Voidreaver. His PvP gear was mostly S1/S2 when he quit.

So yes, boomkin can be viable in pvp and pve. I think for pvp you are better off with 5 or 4+healer. PvE 1-3-1 would make the most sense. Treants are evil, evil creatures at lower levels. Fear is an issue for all MBers, even the shaman.

I have a RAF druid team + my kids both play druids for 4 total I plan to play with my pally as 4 boomkin/tank with 1 out of moonkin for heals. They are scattered in levels now so I haven't had a chance to try it yet with all 4.