for my $row (@out){
    local $" = "\t";
    print "@$row\n";
}
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See perlvar for details.

If you want to iterate over it:

for my $row (@out){
    for my $col (@$row){ 
         # do something;
    }
    print "\n";
}
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for $row ( @out ) {
    print join( "\t", @$row), "\n";
}
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Another way:

$, = "\t"; # Output field separator
for $row ( @out ) {
    print @$row, "\n";
}
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Update: moritz is right, $" is better than $, ($, leaves a TAB bebore NEWLINE)

moritz is right, $" is better than $, ($, leaves a TAB bebore NEWLINE)

Not at all. Just use $, in conjunction with $\.

{
   local $, = "\t";
   local $\ = "\n";
   for my $row ( @out ) {
      print @$row;
   }
}
[download]

Of course, the join method much clearer.

Joins are a little more expensive; If the number of elements in @out (num lines * num items per line) is in the millions, using $" is noticeably faster. If the expected size of the output will not be this huge, however, using join is much cleaner, as you pointed out.