I knew my reply will be heavily hammered by rubyists. There is nothing wrong in the language but I think that shell tools should be written in C or in some other low level language without complex dependencies over ruby or java or python etc. or any other non-default installation stuff
I like this idea a lot.
But why on earth it is written in ruby?! - I know the answer and it is "ok". But it is probably the reason why it won't never gain huge momentum, prove me wrong :)
http://www.privoxy.org/user-manual/startup.html
Edit, actually I am not sure:
http://www.privoxy.org/faq/misc.html