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[1] http://timepedia.blogspot.com/2009/08/on-reducing-size-of-co...
[2] http://code.google.com/p/google-web-toolkit/source/detail?r=...
I thoroughly recommend taking the time to read it.
Sure there are browsers that can't decompress these streams, but your webserver already knows when to send the full (but minified) JS instead. Its all handled automatically.
"The packed versions require non-trivial client-side processing time to uncompress (unpack) the code whereas the minified versions do not."