Interesting. Running the same test on my ActiveState Win32 Perl 5.8.2 build 808, I get results indicating that -1 more reliably accesses the last element of an array.

The following one-liner was run repeatedly with  $[ initialized to different values:

>perl -wMstrict -le
"$[ = 100;  my @ra = qw(a b c d e f);
 print '$[: ', $[, '  -1: ', $ra[-1], '  $#: ', $ra[$#ra];"
$[: 100  -1: f  $#: f
[download]

Output of successive runs of the one-liner:

$[: 100  -1: f  $#: f
$[: 1  -1: f  $#: f
$[: 0  -1: f  $#: f
$[: -1  -1: f  $#: f
$[: -6  -1: f  $#: f
$[: -7  -1: f  $#: e
$[: -11  -1: f  $#: a
Use of uninitialized value in print at -e line 1.
$[: -12  -1: f  $#:
Use of uninitialized value in print at -e line 1.
$[: -99  -1: f  $#:
[download]

Perhaps more support for the don't do that part of the discussion in the docs about assigning to  $[ a value other than 0?

(BTW, the latest perlvar sez wrt  $[ that As of release 5 of Perl, assignment to $[ is treated as a compiler directive, and cannot influence the behavior of any other file, so old code that plays too fast and loose with  $[ may be broken anyway.)