In a longish thread on fixing the Shaman class yesterday, Tseric stopped by to comment on concerns that Shaman are mana-inefficient and can't do much of anything while OOM. I find it fairly informative regarding the devs' stance on Shaman and mana, so I'll quote it in full:
While I can't really comment on your suggestions, there are a couple points which I'd like to address from what I know. I can certainly take the remaining feedback from the thread, at any rate. ;)
Mana efficiency for Shaman has always been on the low side. You might be arguing one of the defining characteristics of the class. However, they are also a melee class, so they can do more without mana than a mage or priest. At the base, you can apply the quoted statement to any mana-using class, but at the same time Shaman do not come out at the bottom of that pile.
Q u o t e:
Shaman need more mana regeneration. Once their mana runs out there's not much they can do.