Google likes javascript.

Actually the way they assign rankings and weight factors is based on a number of factors, they calcualte keyword density, noun and verb density, the ammount of H1, H2, Bold, Italic, Etc
Including javascript is not really that much of a jump, google has been working on indexing javascript for a long time, as well as flash, but the technical problems neutron have described are why it is taking so long and its still only experimental.
As for the ammount of javascript I was SEOing a site that had a dynamic date so google crawled it every day cause of the "fresh content"
I did some testing on the ammount of JS include files and yes it did make a noticable and measurable affect on the rankings, I tested it for quite a while.
If a site has javascript it is more likely to be newer and more advanced than a static HTML site, so it makes sense to give it a slight serps boost.