Just finally breaking 280 (actually saw 318 for a sec) Mh/s w x2 5770 in a 2,1 MacPro 8 core using bitMinter client n fiddling a bit...looking to bootCamp Win7 then Linux n drop Windows I guess.  My 5970 is on its way though, so should be close to 900Mh/s by next week and gonna build a beater rig w an old tower maybe or recycled tower.  I could probably farm my MacBook Pro w the MacPro but I just learned of mining in the beginning of March.