1. OS4 pre-release (have an old pc that has been turned on 3-4 times since I got the pre-release, mainly to use home banking which needs JAVA).
2. Because its the best available OS for my A1

Having used AmigaOS since '88 it feels like the natural choice. I have used other OS' aswell but always missed my Amiga when I sat in front of an Winblows machine.
My next computer will be an... Amiga. Whether it will be the MicroA1-I, or a next generation machine I still don't know. That will depend a little on software availability (seems we wont have a decent browser when the MicroA1-I is released, so my parents wont have much use for my A1-XE yet).