Despite what is being stated here in other answers and totally contrary to Google's own FAQ, a Google employee named JohnMu answered a question recently in Google Groups about how the GoogleBot came to follow a non-existent URL. (The actual URL was contained within the jQuery code itself and the GoogleBot DID try to follow it.)
jQuery causing 404 errors in Google Webmaster Tools
Google Employee explains how JavaScript and jQuery are indexed
Apparently, Google does attempt to index your JavaScript.
Quote Google's JohnMu:
"I would also recommend not explicitly
disallowing crawling of the jQuery
file. While we generally wouldn't
index it on its own, we may need to
access it to generate good Instant
Previews for your site."
JohnMu later in the same thread...
"Additionally, we're constantly working
on improving processing of JavaScript
for web-search in general, so if you
use jQuery to pull in content, and the
jQuery script is disallowed for
Googlebot, then we would not be able
to look at that at all."