Until about a year ago, I never even considered purchasing a Mac.
I needed a new laptop, and decided that the 12" PowerBook had the perfect weight/battery life for my needs. I hung around the Apple Store for a little while, played with OS X, and decided that I could live with it.
Now, just over a year later, I find that I use my PowerBook for everything! I love being able to open up the Terminal and use my Unix knowledge, and when I'm done return to an excellent interface.
I still use my Windows machines when the task at hand can be more quickly or easily accomplished using that OS, however the majority of my work can be done just as easily on OS X.