Here's another data point:

I downloaded jquery-1.3.2.js and jquery-1.3.2.min.js from http://docs.jquery.com/Downloading_jQuery#Current_Release

> wc -c jquery-1.3.2.js

120763

> wc -c jquery-1.3.2.min.js

57254

> java -jar compiler.jar --js jquery-1.3.2.js | wc -c

55340

Using Google's compiler saves an additional 4% over the existing minified version

(disclosure: I used to work for Google)

I definitely plan on switching jQuery over to using this compressor - excited by the output. However it appears as if it crashes when you push the latest nightlies of jQuery in. Not sure what's up with that.

Out of curiousity, I threw together a quick comparison using SlickSpeed and the latest jQuery/Prototype frameworks.

http://bit.ly/1Ei4o8

If someone wants to contribute a jQuery version compiled with advanced opts, I'll be happy to add it to the list.