What's ironic is that a Mac is one of the best possible machines you can get to run Windows 7. I've run some of the pre-release versions, and we've been working with the release version for a few weeks, and Windows 7 on a Core 2 Duo or Quad Core Mac just flies. Microsoft is unlikely to say so, but they love selling full Windows licenses to Mac owners. That's far more profitable than selling a bundle edition of Windows to a cheapo computer manufacturer, or selling an upgrade to someone who owns a Dell.
The Mac camp is poking at Windows 7, but on a technological level, on a new machine, there's very little to poke at, in all honesty. It really is a decent OS, and if Windows is the way your brain works, it's a good choice. Certainly a far better idea than sticking with Vista. (If a Mac is the way your brain works, as mine is, stick with Macs and you'll still be happier.) Note that if your Windows box is old enough to have come with XP, it may not be suitable for Windows 7; if it's a year or two old, it should do fine.
Where the criticisms are valid is the nightmarish upgrade path, though. While Apple has one Mac OS X 10.6 package, at one price covering all the features in the OS, Microsoft has once again released a loony array of different editions. What's worse, whether you can smoothly install Windows 7 over your existing Windows computer setup depends both on which edition you had before and which edition you choose to buy now. If you had Windows Vista Ultimate and you choose Windows 7 Professional (or, just as likely, your IT department chooses it without asking you), you can't just install the upgrade. You have to back up your data, wipe your hard drive, install the new OS, restore all your data, and then individually reinstall all of your applications from the original CDs or downloads, and that's just nuts.
Glenn Fleishman had a good piece in TidBITS last week about the Windows 7 upgrade weirdnesses. It includes Walt Mossberg's crazy multi-column chart that shows what your upgrade path will look like.