I can already use a shared jQuery or other library, I don't need Page Speed for that, though if Google can discover that the library I have is actually exactly

I can already use a shared jQuery or other library, I don't need Page Speed for that, though if Google can discover that the library I have is actually exactly the same as one it hosts on it's own CDN, then of course it can rewrite my page to make use of the CDN one. My javascript on the other hand is (likely) not useful to someone else's site, and therefore that example isn't a very effective use. I just remembered that Page Speed also has an image optimizer, which could be very effective here. The search example obviously has some flaws, because yes, caching is likely to be effective at least for a few seconds (think Twitter search). What happens in the case of protected resources where a session cookie or XSRF token make the page uncacheable?