Serving javascript libraries from the CDN rather than your personal server includes tremendous advantages. Less work with your server, possibility for that CDN to possess a copy nearer to the consumer than your server, but many importantly a strong possibility that your user's browser already has it cached from that URL. The final one means less total work with everyone, therefore it is clearly victory throughout, and it is much more likely the greater frequently we (designers) depend about the CDNs for everyone our javascript.

However the popular javascript CDNs (Google, Microsoft, others?) only host a small amount of files. For other people we now have the option of hosting them ourselves, or ... while using source control server like a type of CDN. It's unlikely Github or similar includes a geographically distributed cache of files enhanced for serving globally. But when it is common practice, then there's a good chance the user's browser may have it cached. The argument of off-loading work from your servers to github is just valid if Github has voluntarily volunteered to get this done.

So, could it be common practice? Should we encourage one another to get this done? Does Github mind? Have they got the official policy mentioned?

You shouldn't do this for JavaScript files should you worry about performance or IE9 compatibility.

GitHub does not serve its "raw" files having a far-future expires header. Without the potential of mix-site caching, you lose the greatest advantage of utilizing a public CDN to host your JavaScript. Actually, using GitHub like a CDN is going to be reduced than hosting the files by yourself server after each user's first request the file (presuming you configure caching properly in your server).

One other issue is the fact that GitHub does not serve "raw" files having a content-type header that suits the file's actual MIME type. In IE9 (and possibly other browsers/proxies/fire walls/etc), JavaScript files that are not offered using the correct content-type are blocked automatically. You can observe that for action about the BlockUI demo page, for instance:

enter image description here

I'd never depend on GitHub like a CDN for my projects because you've got no guarantee the files is going to be there, named exactly the same way, later on. With Google/Microsoft you will find the commitment both companies designed to host the files inside a certain way, with GitHub you simply have hope that it is going to stay this way.

It was lately requested in github's support forums, and also the official answer was it's ok.

With that said, To be sure along with other solutions: github never was really meant to become a CDN, while Google and Microsoft have specific infrastructure for your.

I am doing the work for several weeks now, had some concerns first but it is totally awesome for those who have no issues with your files being openly available, use minified versions should you care.

But nonetheless - Google &lifier MS rule the area for jQuery &lifier jQuery Templates - and so i rely on them for your.

Connecting to GitHub "raw" files has some issues as layed out by Dork Ward's answer.

It is best to consider GitHub Pages being an option.

Look at this article:
GitHub like a CDN. Cache your Javascripts, Stylesheets and Web Assets with GitHub Pages.