Good news from the European Forums today; according to Community Manager Vaneras, the development staff is aware of the poor performance of Druids in Arena and are “looking into” possible improvements:
The Druid class is somewhat under-represented in the Arenas, which there of course are various reasons for. The developers are looking into the Druids overall performance in the Arenas, so I would say that it is too soon to give up on your Druid just yet.
I personally enjoy PvPing on my Druid, but I play mostly in the battlegrounds.
Vaneras made a similar post in the European Rogue forums today, responding in much greater detail to a post which laid out several of the perceived issues with Rogue Arena viability.