From "Is jQuery too big for mobile?":

Amazon famously found that every 100ms of delay in the load time of amazon.com cost them 1% in sales. If we accept this finding verbatim, it would mean that including jQuery decreases your mobile sales by 3%. That sounds bad, but you have consider the flip side as well; if using jQuery improves your productivity enough to generate 3% more revenue, in theory including it is worth the trade off.

I like this sort of approach. The article's conclusion: "there's almost certainly something way more important to the efficiency of your application than whether you use jQuery".

I was also surprised to learn that CDNs have a much lower hit rate than I thought!