Here's one for the obscurities wishlist: our NetCaches don't recognise integer representations of IPs. Instead of interpreting 3263497985 as 194.133.7.1, for example, they look for www.3263497985.com.
Although nobody in their right mind would want to do this, people do use it when they want to obscure the tru source of a URL (yes, mainly in dodgy newsgroups, I know).
Later,
Alex.