I'm not a Mac user but I've had this debate with an avid Mac user a couple of years ago. His position was in-line with RacerX's, in that Apple is a hardware company and that's their bread and butter. My position is Apple should sell OS X for Intel as a standalone product offering. Continue to produce Macs but sell OS X standalone.
Given the discussion about how the iPod got some to purchase Macs (presumably those who would not have purchased Macs otherwise), I see OS X , as a standalone product, functioning in a similar fashion. As it stands today, someone looking to get away from Windows must consider the cost of a Mac plus the "cost" of the learning curve, data transfer, etc., or they start asking questions about Linux distributions and then get all confused. I speculate, this same person might be open to buying Mac OS X to install on their PC. If they like it, they would be more open minded to Apple products, since their OS X experience would probably be great (leaving some room for problems), and might consider a Mac as their next PC ugrade purchase.
On the flip side, if this person doesn't want to pay the cost of a whole new computer to get away from the frustration with Windows, they won't necessarily be a customer of Apple.
I can see the argument of OS X standalone possibly negatively impacting Mac sales, but I think the iPod example proves this won't necessarily be the case, at least to some degree. I don't think those who prefer Mac hardware today would stop buying Mac hardware, but those not open to Mac hardware today might change their mind once they've had a taste of OS X.
Just my view, as a Linux and Windows user.
Peace...