Microsoft has started to attempt to set the record straight about Vista. At a recent partner conference I attended, they acknowledge they have not been very aggressive at responding to the "I'm a Mac" ads that paint Vista as bloated, slow, and hard to use. I have used Vista for about a year now, and was skeptical at first, but can tell you that it works well.
But not all users can agree.
For those who simply misunderstood, and Vista will work well for them but they have been hesitant, Microsoft is gearing up a publicity machine to answer the Mac, and say proudly "I'm a PC".
And for those have tried Vista, and thought it was bloated, slow, and hard to use, Microsoft has published a nice, concise document that explains how to optimize it. The information is not earthshaking, but is conveniently in one place. You can find it here.
Hope it helps. I cannot say with personal evidence that Vista is better than a Mac, but can say it is an improvement over the XP operating system for my needs.