well for one, as you mentioned, I don't have to worry about this spyware/virus crap and having to reformat my HD every 2 months.
Two, I despise having to wait 5 bloody minutes to do anything on a 3+GHz PC..I boot up and am working under AmigaOS in less than 25 seconds!!!
Three, Blender on my 800Mhz system is snappier to work on compared to my friends 2 GHz PC (of course though rendering times are quicker on the PC)
Three, AmigaOS is my preferred OS for reasons we all know