1. Opened a words file outside the subroutine
2. Passed in letters as array not array ref or string (method wasn't specified above)
3. Case sensitive... I don't match 'Sunday' because I wasn't passed a capital S.
4. Returns a large set of matching words, w/o looking for the longest ones..... that wasn't the "interesting" part of the course for me, so I punted. ;-)

So, here's my first second fourth attempt at 64 chars:

my @letters = qw(d u n s c a e y t);
open(D,"/usr/dict/words") or die $!;

my @words   = f(@letters);
print "$_\n" for @words;

sub f {
#        1         2         3         4         5         6
#234567890123456789012345678901234567890123456789012345678901234
$;=join'?',sort@_,$;;grep{chop;(join'',sort split//)=~/^$;$/}<D>
}
__END__

=head1 SAMPLE OUTPUT
ace
aces
acne
act
acted
acute
ad
ads
an
and
[SNIP]
uneasy
unsteady
[SNIP]
[download]

#        1         2         3         4         5         6         7
#234567890123456789012345678901234567890123456789012345678901234567890
+123456
$,=join'?',sort(@_),'';grep{chop;$;=join'',(sort(split//,$_));$;=~/^$,
+$/}<D>
$,=join'?',sort(@_),'';grep{chop;(join'',(sort(split//,$_)))=~/^$,$/}<
+D>
$,=join'?',sort(@_),'';grep{chop;(join'',sort split//)=~/^$,$/}<D>
$;=join'?',sort@_,$;;grep{chop;(join'',sort split//)=~/^$;$/}<D>
# with japhy's help...
$;=join'?',sort@_;grep{chop;(join'',sort split//)=~/^$;?$/}<D>
@_=sort@_;$"='?';grep{chop;(join'',sort split//)=~/^@_?$/}<D>
# with dragonchild's help, and a 'perl -l' trick:
@_=sort@_;$"='?';grep{(join'',sort split//)=~/^$\@_?$/}<D>
# stealing a bit from gbarr
@_=sort@_;$"='?';grep{(join'',sort/./g)=~/^@_?$/}<D>
[download]

-Blake