A commenter at sitepoint noted the positive point about Google open sourcing Closure. I think it's a good point. It leaves room for people to review, critique, and help improve things.

I thought the more interesting thing about Closure was the optimizer (and I wonder if the optimizer offsets any of the issues described in this critique.)

Regarding the library, I think the interface is more important at this point than the implementation. The latter can be refactored, while the former will always be there.