Yes I've found that too. Our single-page-style apps would do better to bundle all our dependencies together into a single request to our own servers.

However say for content-based sites, the theoretical ideal is that the content should be delivered and usable without the inclusion of fooLib.js (which folks say should even be included as late as just before </body>), so a delay from a CDN would not necessarily cause any apparent "hang". Again this is the ideal and admittedly I've never got it right.

You could probably wire something up in JS to handle it with reduced timeouts, e.g. an AJAX call that automatically fails after 50-100ms and proceeds to load the local version.