If Mac came out with a $600 notebook, I might look into buying one.
But then I realized that it would be filled with pretty bad hardware :( A windows notebook that I bought for $750 has the same hardware (give or take a few MHz and a gig more of RAM) as the $1200 MBP.
If Mac could get over their overcharging for hardware then they could increase their market share, but they would lose the exclusive feel that they have offered their customers.