For those of you who are looking for a BioShock demo on the PC, it is in the works and will be out later this month. I'll give you more details about it tomorrow.
but choosing the PC experience because of the keyboard mouse means using a smaller screen, sitting at a desk, getting stereo sound. Choosing the 360 experience comes on a 46" TV, 5.1 sound, a comfortable couch, and a controller.