and run it on your website and google for caching web requests.
Hope that's not too technical. The problems with using external resources is usually:
* you trust the external resource. (security)
* you realise they can disappear (sustainability)
* you realise they can make changes to the file (see trust)
* you realise you are directing traffic from your website to theirs (responsibility)
I think that is not a problem with google, but for example 'hotlinking' to images from another website (point to the image on an external website) would be a bad idea. They could easily replace an image with an offensive one. Also I've seen it used to attach an external site by overloading it with traffic, which obviously is not responsible (could be criminal).