[thirdtruck]

It is a blatant imitation[1]. At the same time, the design is incredibly refined, so there's only so much room to move away from without making sacrifices solely for the sake of differentiation.

EDIT: [1] According to a comment below, it's a straight-up copy of the CSS. That goes well beyond "blatant imitation."

[tghw]

Imitation is different than directly copying the CSS. They copied the CSS.

[zo1]

Which is totally fine for development purposes (prototype) and work in progress mockups. But they should have changed it before putting it on a public-facing .com domain.

[cheald]

I'm going to suggest that it's not even good for prototype work, because it invalidates any claim to clean-room implementation and makes it very easy to cross the line between original work and ripoff.

[thirdtruck]

Oh snap. That is a whole different story.