If you look at the second conditional comment, it will not be parsed as a comment in browsers without conditional comment support.

In other words, it will correctly use jQuery 2.0, like any other browser without conditional comment support.

It's a conditional conditional comment. I feel ill.

It's known as a downlevel revealed conditional comment. You will see it in use in the HTML5 boilerplate. That said, I echo your sentiment, it is an immensely horrid syntax. For more info: http://css-tricks.com/downlevel-hidden-downlevel-revealed/

You do realize that IE 10 will be supported by jQuery 2.0, right?

You do realize that saying "you do realize, right" is about the rudest and most condescending way to pass on information, right?