This is huge. I've been wanting Closure as OSS ever since I interned at Google. The compiler is optimizing -- it is not a simple obfuscator like YUI Compressor.
YUI Compressor is not a simple obfuscator. It does quite a few safe optimizations, but it doesn't do anything that could break your code.
YUI is not just an obfuscator--it also minifies and dramatically reduces file sizes. Closure seems to outperform it in most cases, but to say that it's a "simple obfuscator" is a great disservice.
You're right, I meant "minifier".
Looks very very cool. Unfortunately quite a few of the examples didn't work when I tried them in Safari. Not sure why :/