Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
As a BTO option, I do not see why not. I installed a WD 320GB unit in mine as soon as I got it home from the Apple Store.
 
They're going to have to start providing larger HDDs since everything is getting larger.

I can see a 320/5400 being standard, and then having 320/7200 and then the larger drives as BTOs.

I dunno, that's just my thoughts.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.