This one is one I've been using in production for a while, and seems to hold up well:
my $url="http://proxy.aol.com:8080/login"; my($host)=$url=~/http:\/\/([^\/]+)/;
Update: Sorry, I'm a moe - I forgot to add the point of this post in my example!
Good judgement comes with experience. Unfortunately, the experience usually comes from bad judgement.