I've also had a need for this sort of functionality although not necessarily in an OO context. For example, say you want a sub to be called in a manner similar to the built-in sort (most likely in a module). This example (toy) code throws an error:

#!/usr/bin/perl -w
use strict;

sub func (&@) {
  my $func = shift;
  foreach (@_) {
    $func->($_);
  }
}

sub func (@) {
  foreach (@_) {
    print $_;
  }
}

my @list = ('bob', 'sally', 'joe');
func { print "!!!$_\n"; } @list;
func @list;
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It would be quite nice to be able to do this sort of thing. If you didn't need the prototype to treat a block as a sub things would also work out. It is also easy to work around this issue by taking an explicit reference to a sub but the block is much more natural and provides subs that are similar in use to the built-in functions. Perhaps I am missing something obvious...