This is completely ignoring the fact that windows aren't viewed in isolation. The thick border makes it easy to see where one window ends and another begins.

I find that OS X windows tend to blend into each other a lot more because they lack the border and have much softer shadows.

The only thing I am sure of after reading this article is that I really cant stand the term "User Experience" and the abbreviation "UX".

The thicker border provides a larger area to hit when trying to resize a window.

If you don't like the transparency, turn it off.