At J! and Beyond, we discussed ways of implementing jQuery in Joomla 3.0. Here is what we have so far:
A minified copy of jQuery 1.7.2
A file with jQuery.noConflict();
An additional method for JHtmlBehavior (would require Platfrom merge, unless we have a standard way of doing this in the CMS library)
This approach works, but it is sub-optimal as you have to incur the overhead of two HTTP requests. There are two workarounds we could pursue:
Manually add jQuery.noConflict(); at the end of jquery.min.js. We would have to do this every time we update jQuery. This is what WordPress does.
Add new code to JDocument and JDocumentRenderer that would allow declarations to be added immediately before or after a script is loaded. (I believe @beat mentioned he had a pull request for this on the platform)
Another thing we may want to consider is adding an option in Joomla that will let you specify a CDN copy of jQuery to use in place of the local one.