When Apple announced the switch to Intel, I speculated that Apple would benefit from the purchase of Macs by Windows users. I was wrong about some details (like the ability to run Windows apps under OS X), but things did develop along those lines.
Apple changed the game a bit (in my favor) with the announcement of Boot Camp, and I refined my prediction a bit, speculating that Windows users would, to some degree, be inclined to buy Mac, even for the purpose of running Windows, and that even a small percentage of "switchers" would be a huge gain for Apple.
A few years later, I claim vindication, with both anecdotes and facts:
* The "Windows apps on Mac" problem has been addressed, to some extent, by Parallels and VMWare Fusion, which do not require booting into Windows (to the exclusion of OS X) to run Windows apps.
* I have many acquaintances who have switched to the Mac, in spite of distinct aversion to the Mac before OS X and the Intel switch.
* There are a lot of PCs at my current employer that are Macs running Windows all the time, including, I'm amused to note, machines on the desks of our IT support staff. OK, they're running Windows, but they are (high margin) sales for Apple.
* Apple is enjoying greater market share,
Windows 7 may convince Windows users to stay with Windows, but that does not exclude them from buying Macs to run Windows 7, and there are still good reasons to buy a Mac even to run Windows 7: it's elegant, high-performance hardware for your needs, and, should the need or desire arise, there is no need to buy new hardware to run OS/X.
Yes, you could buy cheaper hardware to run Windows 7, and many (most?) will, but it has been demonstrated that Apple does have a price advantage at a certain (high) level of feature specifications, and, not accidentally, high margins.
It doesn't have to be a lot; as I said way back, a small number of Windows user, even if they choose to remain Windows users, is a big percentage boost to Apple's hardware share, and to their bottom line.
(*) Apologies/tip-of-the-hat to John Gruber at Daring Fireball