From an engaget.com interview with Bill Gates: http://www.engadget.com/2008/01/07/bill-gates-the-exit-interview/

On the Windows side. One hundred million licenses, obviously that's an enormous amount. But I think in the last few months, especially within from media and the blogosphere and all of these different places, Vista specifically is getting hit really hard with a lot of negative PR — a pretty big backlash from users who are downgrading to XP. Or at least a lot of people talking about downgrading. Do you feel like right now you are leaving under a cloud? That the company's core product not meeting consumer expectations?
I wouldn't say that. Any version of Windows is going to have lots of great new things that people use and things that are tough. With Vista, a lot of it's the transition from XP to Vista. Did we get the device drivers ready in the right way and time? Did we make it easy to do the upgrades as well as we should? When people get up and running on Vista they are basically quite happy. Not perfect — but quite happy. It is that transition where we definitely need to get a better job up on that piece.
Now, in time, more of those drivers are becoming available. It is definitely a product where we look back and say, okay, a lot of good things but we are going to change the things where it just didn't become trivial to step up to the new version. That's always been hard with Windows and we're looking at some of those challenges and why we didn't think they'd be as hard as they were — and making sure that we do better at it. The feedback is important to us, but it is a product that has lots of good features. I encourage people to use it! We are proud of the features in there!
Well, of course! But are you personally fully satisfied with it?
I'm never fully satisfied with any Microsoft product.
Like the saying, "Software is never complete, only abandoned"?
There are always the features that I wanted to get in, or the things that I wish were a little more polished. The people who are good in these companies are really sort of ridiculously demanding people. They have to sort of know when to back off so that thing can eventually ship. But I look at any product — and I'm better at Microsoft products — and say what I wished what was better about the product.