An odd discovery today – if you don’t specify a protocol in your links, the browser apparently suppose it’s the same (be that http or https) as the current page. You can se it in action on Slashdot by viewing their source – none of the regular links has protocol specification – they just start with two slashes and the hostname (ie. //netfactory.dk/).
In the case of Slashdot I suppose they don’t use it to save bandwidth, but in most cases it’s probably useless.
(Discovered by mkyed).