1) It runs on multiple platforms. It feels more future proof because I can buy x86, AMD64, PPC, ARM, whatever in the future and still be able to run my OS of choice on it.

2) It is evolving rapidly. Mac OS X is great, with the near yearly updates, but Windows is largely stagnant.

3) Upgrades can be very cheap, and when using a meta-distribution like Debian, Gentoo, Ubuntu, or Arch those upgrades are very easy and ongoing.

4) Its future direction is not controlled by one person, or one company.

There are more reasons, but I don't want to sound too much like a fan boy. Hopefully my life will be long, and I want to keep as much flexibility in it as possible, and Mac OS X and Windows just seem too limiting.

Anyone else notice how the poll question is different than the question that appears at the top when you post a comment? The comment question is: If I could only choose one solar powered laptop to take onto a desert island, what os would it run?

My answer to that question would probably still be Linux because it comes with a lot of developer tools which give me a lot more flexibility to entertain myself than base installs of OS X or Windows.