Asking from nearly complete ignorance here but: with a JS compiler/optimizer like Google's Closure [1] wouldn't it be possible to still use jQuery but have all the unnecessary code that's not used striped out?
That might be the case. This blog post [1] shows some examples of what the advance optimizations do and it seems that, while it'll shorten everithing up, things that are put in the global namespace (window) will not be stripped even when they aren't called. As jQuery adds the 'jQuery' and '$' variable to the global namespace and all it's functions are attached to that object, I would assume that the Closure compile connot remove any of them.
Of course, this is all pure speculation, it'd be much better to test this out.
Closure can definitely remove functions that are never called - but I wonder if its static analysis can figure out jQuery style code. My guess is that it'll do a decent job, but jQuery would need many changes to get it to compile.
[1]: http://code.google.com/closure/compiler/