Not entirely sure why you'd want too - unless your into graphic design. But then again, all the old progs written for MAC for the graphic design crowd are now better on windows. The arguement about Mac's being virus free is tosh but at least they are good to look at.
It was a bit confusing at first, kind of not windows but not a straight forward linux.
I like the fact everything just works all the drivers are preloaded with the os so when you install some new hardware it all works.
I dont like the fact that they cost the GDP of a small country and are now based on PC components so there no CISC vs RISC performance advangtage, also third party software can be an ass to install and get running correctly.
Virus free and security hole free is a load of carp as boney_m said, despite what the apple people will say.
I liked it more than Vista though (although SP1 is now out i have not played with that yet)
I liked it quite a bit less than XP
To be honest now i've had it for a while it is what it is JALP (just another linux platform) and thats it better for some things not as good for others, i ranked it about the same a GOS.
but then if you dont like OSX just install XP or a linux os.