"http:apple.com" and "http:/apple.com" both load and display the incorrect URL in the URL bar.
"http:///apple.com" is converted to "http:/apple.com" for reasons I don't understand (maybe NSURL does this).
In IE, all of these loads fail. In Firefox, they are all converted to "http://apple.com". Firefox's behavior is better. For known hierarchical schemes such as http, the URL should be treated as hierarchical no matter how many slashes there are, and normalized accordingly.
Just a side note. This may also be related to file: URLs behavior. Last I checked (long ago), it seemed quite funky in Windows Safari.