Just a short note to say that I bought my Mac only because of the release of OS X and the developer tools that came along with it "as standard". I do love the GUI and all the media applications that came with it, but it's what's under the hood and how it's all been put together that I find really exciting.
I think OS X is great for people that want to develop software and want to work in the "open" environment. I can download loads of UNIX software source code and build it locally, such as GNU software and binaries such as MySQL are turning up on Web sites more and more. For me Java software development is a breeze and with a 1.3 SDK installed as part of OS' architecture I have very little problems having fun developing software that can be used on other platfroms as well.
In the past I looked at buying a Mac but never got a warm feeling that I'd be able to do what I wanted to do with it. I think the last time I booted up into OS 9 was about two months ago and that was only to check software update!