Since 2006, Apple's "Get a Mac" ad campaign featuring Justin Long as a relaxed, hip Mac and John Hodgman as a stuffy, stressed-out PC have poked fun at the PC industry and Windows in particular. For years, Microsoft ignored the campaign, but in September 2008, Microsoft launched what is reportedly a $300 million ad campaign aimed at, to quote the internal Microsoft email about the campaign, telling "the story of how Windows enables a billion people around the globe to do more with their lives today."
As "an icebreaker to reintroduce Microsoft to viewers in a consumer context," Microsoft made a set of ads featuring Bill Gates and comedian Jerry Seinfeld (whose character in his eponymous TV series was a highly visible Mac user). The ads were, at least for me and nearly everyone I've talked with, essentially inscrutable. The first featured Gates and Seinfeld buying shoes, and the second showed them living with a supposedly stereotypical American family. Perhaps I'm just not sufficiently sophisticated about advertising or utterly not the target audience, but they made no sense to me. (Clearly I wasn't alone, since Microsoft pulled the campaign abruptly - after having reportedly paid Seinfeld $10 million for his work.) The followup "I'm a PC" ads were far more powerful and effective, and at their best make Apple's ads seem smug.
It's not unusual for one company's advertising to take on the competition directly, but it's far more so for the target to respond with its own ad campaign. Doing so risks cementing the negative points made by the initial campaign. But we're stepping into even more rarified advertising territory now, since Apple has just released a new "Bean Counter" ad that tweaks Microsoft for spending $300 million on advertising rather than putting it into Vista development.
Although there's a risk that Apple's "Bean Counter" ad could be seen as relying on a reference that only loyal Apple fans would possibly understand, the ad continues to hammer home Apple's criticism of Windows Vista, and I suspect that anyone not following the Apple/Microsoft ad wars will see it purely in that light. And that, I'm sure, is just fine with Apple.