Like you, I am a "multiplatformist" (nice term, by the way). I run both Windows 7 Ultimate and OS X, although I run them both on my MBP and not on separate laptops. As noted in my last post, I don't understand the Windows bashing that we see so much of because Win 7 is really quite a nice OS, exponentially better that Vista, which I did bashed.
How a computer performs doesn't affect my happiness exactly but a poorly performing one does tend to raise my frustration level, which, I suppose, does affect my quality of life to one degree or another. On a more basic level, I agree that computers are only tools and have little or nothing to do with my sense of self-worth.
