After a couple of teasers starring Jerry Seinfeld, Microsoft is airing some new ads that take Apple's "I'm a PC" out into the real world. So instead of John Hodgman's dorky PC character (who is parodied in one of the new ads), they've got all sorts of people -- basketball players, actresses, scientists, fashion designers, etc. -- proudly declaring "I'm a PC". As Michael Sippey mentions, the ads do communicate a "message of joy and abundance and widespread use of Personal Computing", but they're not "great".
I briefly worked for a design firm in the late 90s that did a lot of advertising work. One of the hard and fast rules in the office -- which was taken from a book written by a successful ad man whose name I cannot recall -- was that if a company was #1 in a certain space, their advertising should never ever mention the competition, not even in an oblique fashion. And even if a company was #2, they should do the same and act as if they were #1.
That's the problem with Microsoft's ads. They're still #1 and the bigger company, but by referencing Apple's successful ad campaign, they're acting like Apple is #1. (John Gruber made this same point the other day.) The ads fail because they serve to remind people that Apple comes up with good ideas that Microsoft then takes and shapes into something that so-called "normal people" can use or understand. Except that this isn't 1993. With the iPod, iPhone, iMac, OS X, the Apple Stores, and the iTunes Store, Apple has their finger firmly on the pulse of what normal people want and Microsoft's recent attempts (the Zune, Vista) to keep up by emulating Apple have failed. If MS had created the "I'm a PC" message on their own, the ads would be great, but these copy-and-paste ads lack soul and are merely "eh".
What's interesting is that with the I'm a Mac/I'm a PC ads, Apple mentions Microsoft explicitly, over and over, proving the old adage that rules are made to be broken. What works in Apple's favor is that they are the #2 company and were clever about how they attacked #1. Microsoft's hamfisted ads are almost saying to Apple, "nuh-uh, my mom thinks I'm cool" while the image of Hodgman's frumpy PC is hard to shake and makes Windows seem lame without being overly insulting about it.