What do you use to minimize and compress JavaScript libraries?
I've used YUI Compressor for a long time and have had no problems with it, but have recently started using Google Closure Compiler and had some success with it. My impressions of it so far:
I've moved over to using Google Closure Compiler in simple "compilation" mode, because it slightly outperforms YUI Compressor in general. I have used it considerably less than I have YUI Compressor but from what I've seen so far I'd recommend it.
One other that I've yet to try but sounds promising is Mihai Bazon's UglifyJS.