Not sure what Mac on Linux is like.
I was thinking more of using a mini as a sort of smart terminal downstairs. Running the local Apple applications and then remote X windows from the Linux box when I need more horsepower or an application that is not available on the mini. If I need access to OSX from the study then I can always remote the Mac using the OSX VNC server or something. The only issue I see with this is that I have heard worrying things about the X server implimentation on OSX.