Over on Toskk's forum Gurnsey has an interesting question: is the Wolfshead Helm worth looking at? That's an old level 40 crafted item which has a nicely scaling on equip effect:
When shapeshifting into Cat form the Druid gains 20 energy, when shapeshifting into Bear form the Druid gains 5 rage.
It still works; seems powershifting isn't quite dead after all. His guess is at level 80 the energy is good for +10% DPS compared to +6% DPS for a top end level 80 helm.
Even if it works I'd never use it. I always hated powershifting, and you have to assume if this technique caught on Blizzard would nerf it. But I love seeing people get creative like that.