At the risk of unintentionally offending someone (apologies as needed), perhaps a pragmatic approach?...
If you compare pricing on MACs vs. PCs with near identical hardware, for many (myself included) any discussion ends right there. Not being cheap as much as practical: if money was no object, I'd just pay somebody else to do it, making any claims of "ease of use" or efficiency etc irrelevant.
The same sort of approach acts as a bit of a reality check regarding Vista... My eldest grew up with PCs, and sees them purely as tools. I set up Vista on his new laptop, and after a few weeks he can't find or tell the difference compared to his desktop running XP Pro. While I certainly know the differences, along with all the pros and cons, to him and I suspect millions of daily users like him (who greatly outnumber enthusiasts) the whole discussion is totally irrelevant.
RE: Shadow Copies... Not a lot of info out there, it is possible to manipulate the shadow files via scripting but otherwise not a lot of uses other than system restore. Unlike XP, Vista's System Restore actually does restore the hdd, and *most* of the registry -- for maximum safety use Erunt before creating the restore point. Shadow copy files are in a different format than anything else, so as soon as a non-vista OS looks at the drive, they're gone, as with multi-boot PCs.