The article starts off with a discussion of Windows Vista and right off the bat Mossberg questions if buyers can be confident in moving forward with a Windows based PC purchase.  He then outlines two significant downsides of Vista PCs:

"Whew! The new Windows Vista operating system, five years in the making, is finally out and preloaded on new PCs from every major Windows computer maker. After months of uncertainty and delay, you can go forth with confidence and buy a new computer, right? Well, it's not that simple."

"Last fall, I advised average consumers with aging PCs to hang on until new Vista PCs emerged, rather than trying to upgrade existing models. I still believe that was the right course, because Windows upgrades are so tricky. But it turns out that even new Vista PCs have two big downsides."

The two Vista downsides: security and software/hardware problems
Mossberg states that despite being a replacement for XP, Vista still needs a third-party security program.  He also describes how software and hardware doesn't work well with Vista.  Mossberg tells Windows PC buyers to be prepared:

"So, if you desperately need a new Windows PC, be prepared to be underwhelmed and to be frustrated by incompatible software and hardware. And if you're not desperate, you might wait another six months or so for the software and hardware to catch up -- and for Microsoft to issue some bug fixes."

Buy a Mac instead
Mossberg suggests that buyers get a Mac.  He gives his opinion that the iMac is the best desktop computer when he states:

"Or you could buy a Mac instead. I still believe the best desktop computer on the market for mainstream, nontechnical consumers is the Apple iMac. It has gorgeous hardware and superior built-in software. Its operating system, Mac OS X, includes most of the key new features of Vista. And the iMac can even run Vista, along with its own operating system, if you need the occasional Windows program."

"Apple has delayed until October the release of its new operating-system version, Leopard. But it's almost certain that any Mac you buy now will upgrade to it smoothly. (See my Mossberg's Mailbox for more details.) And the Mac is still largely free of the security problems that add such hassles to using a Windows PC."

You can read the full article at the following The Wall Street Journal Personal Technology page.