Apparently Open CL doesn't work very well on a Mac, so I was only mining at about 1/4 the rate that the 6970 would get in a PC
Anyone have any idea if Lion will even come close to fixing this? Or is there going to be no change?
Yes it does indeed appear so. Upgrading from SL to Lion has roughly doubled DiabloMiner.app's performance on my MacPro from an average of 140MH/s to 285MH/s with a Radeon HD5870.