Is it people that want to switch away from Windows or switch to Linux?
In my case it was the former, having spent a lot of time on FreeBSD so in 2007 I bought a Macbook Pro running OSX 10.3. This gave me most of what I wanted and when I needed something Windows (XP) specific I installed a VM running under Parallels, then Virtual Box.
I was able to run most of the open source software at that time such as Open Office, Firefox, Thunderbird in preference to the Apple supplied apps.