Honestly, found Elemental to be pretty good whilst leveling. Though, admittedly, that was hitting CD's all the time!
Earthgrab totem is very handy to keep those pesky melee's away as much as possible, as well as glyphing LB to allow you to cast on the move. Don't forget Thunderstorm, Frost Shock and Ghost Wolf to get you away from them. Spiritwalkers grace to heal whilst on the move as well. That's generally my strat.

At level 90 however, its definitely one of the weakest. Nearly every move of yours can get interrupted and/or silenced and leave you like a sitting duck.

Honestly, since Cataclysm I've mained Resto for PvP. Elemental has suffered a lot, and I am not a fan of the RNG aspect of Shaman Burst damage.

I would say, if you spent the time to really learn Ele PvP, you could turn out quite decent. But if you want a solid PvP experience I'd honestly recommend just going Resto.