Since this is the realm of coding style, it's almost certainly all personal preference. ;>

I know that I tend to prefer using a hash once I get above three or four parameters. Some of the reasons that I can think of why I tend to do so:

• I don't have to remember the order in which the parameters are passed. Granted, I do have to remember the names of the keys, but I think that's a small sacrifice. One can also use the same two or three key names for multiple subroutines ot make it easier to remember.
• Self-documentation. As you hinted at, to me it's clearer what:load_foo(filename=>"bar",template="baz", debug=>1); is doing than: load_foo("bar","baz",1); does.
• It means I can establish defaults for some parameters rather easily. To use the same fictitious load_foo subroutine:

  sub load_foo {
    my %args = ( # Defaults
                template => "zort",
                debug    => 0,
                @_);
    ... # yadda yadda yadda
  }
  [download]

• No reordering. If you're using lots of individual scalars, and you find out you don't need the third our of seven of them -- you'd better make sure you take that one out of all of the places where you call it, or you're up a creek. With a hash, it's not so much of an issue.

*shrug* All of the above are just personal preferences, yes. Do what seems to work best for you.

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'