How about this?

$url=~ m|^(\w+):/*((.*\@)?[^/]+)/(.*)$|;
  $protocol= uc($1);  
  $site= $2;
  $path= $4;
[download]

That would accept everything up till the last '@' as part of the site regardless of any '/' characters that it might contain.

UPDATE: Corrected the '@' that needed escaped