Many important OERs are presented as a mediawiki site, including wikieducator.
Suppose you have developed resources on wikieducator, to use with your own students. So what happens if your connection goes for a week or a month? Of course there is the pdf printing service (which is great!), but what if didn't print, or you want your students to access the material online, and your international bandwidth doesn't support it?
Here is a software demonstrator http://www.ict4e.net/mirror/index.php
For example, here are two pages (measured with Yslow), one with a number of images, the other without significant images:
|mirror without images||mirror with images||original page|
|Page: Main Page||||||Main Page|
So at least it's a saving of 50%, but if you turn images off, you might save as much as a factor of 10 or more.
In Bjoern's view, this may well be a 'sweet spot' application: Very little code, very easy to install (if you have php), but gets you a good set of functionality (transfering data as needed). Of course a few more things would need to be done, such as caching of images, and some page names with special characters don't work yet.
You should note this about wikipedia: "Some mirrors load a page from the Wikimedia servers directly every time someone requests a page from them. They alter the text in some way, such as framing it with ads, then send it on to the reader.", see  and .
The above code only reloads the page if it has changed on the server, but it might still come under 'remote loading'. However, it should be ok if it was on the local network.
You might be able to reconcile this as follows: you could stick the present application onto your public network, but use (e.g.) an Apache .htaccess file to redirect based on IP address: Internal people see the local version (that is remote loaded, but not public), others get redirected to the main wikipedia site.