That's just javascript minimization. Standard way of reducing page load times. It's been around way longer than Google Closure, just look at YUI Compressor.
It may stop anyone from looking at a page's source code, but I'd think most developers would put greatly reducing load times ahead of having your javascript being freely read.
It may stop anyone from looking at a page's source code, but I'd think most developers would put greatly reducing load times ahead of having your javascript being freely read.