Now this is interesting, w3compiler, a self-proclaimed next-generation markup and javascript optimizer.
Unfortunately, it’s a Windows application. What I really want is a standalone compressor/script that will compress on check out from CVS/Subversion (would be nice if it automatically tracks updates to the publish tree). This would be stupendous for webapps. An Apache module to do the same might be interesting, although you’d probably want to cache the resulting JS optimizations.
As far as space saving goes, mod_gzip/mod_deflate probably has you 90% covered already, but it’d be interesting if someone wrote a JS compiler based on real-world JS-engine performance results. You could create different targets for each browser based on those profiles. Also, you could probably get some mean compression (and maybe some additional security) if you had distributions of lookup tables for compression/as pads.
Ahh, if only I had minions to do my bidding…