Contrast Tie::File taking 233 seconds:

use strict;
use warnings;
use Tie::File;

$/ = \96;

my $start = time;

tie my @records, 'Tie::File', $ARGV[ 0 ];
shift @records;
untie @records;

printf "Time: %f seconds\n", time() - $start;

__END__
2008-07-18  14:17       527,999,712 500MB.fixed
               1 File(s)    527,999,712 bytes
               0 Dir(s)   2,320,445,440 bytes free

C:\test>junk7 500MB.fixed
Time: 233.000000 seconds

C:\test>dir 500MB.fixed
 Volume in drive C has no label.
 Volume Serial Number is BCCA-B4CC

 Directory of C:\test

2008-07-18  23:34       527,999,616 500MB.fixed
               1 File(s)    527,999,616 bytes
               0 Dir(s)   2,320,416,768 bytes free
[download]

With a read-seek-write solution taking < 5 seconds:

#! perl -slw
use strict;
use Fcntl qw[ SEEK_CUR SEEK_SET ];
use constant BUFSIZE => 64 * 1024;

my $start = time;

our $RECLEN || die "you must specify the length of the header. -RECLEN
+=nnn";
@ARGV or die "No filename";

open FILE, '+<:raw', $ARGV[ 0 ]
    or die "$!: $ARGV[ 0 ]";

sysread FILE, my $header, $RECLEN or die "sysread: $!";

my( $nextWrite, $nextRead ) = 0;
while( sysread FILE, my $buffer, BUFSIZE ) {

     $nextRead = sysseek FILE, 0, SEEK_CUR
        or die "Seek query next read failed; $!";

     sysseek FILE, $nextWrite, SEEK_SET
        or die "Seek next write failed: $!";

     syswrite FILE, $buffer
        or die "Write failed: $!";;

     $nextWrite = sysseek FILE, 0, SEEK_CUR
        or die "Seek query next write failed $!";

     sysseek FILE, $nextRead, SEEK_SET
        or die "Seek next Read failed: $!";
}

truncate FILE, $nextWrite or die "truncate failed: $!";
close FILE or die "close failed: $!";

printf "Took: %f seconds\n", time() - $start;

__END__
C:\test>dir 500MB.fixed
 Volume in drive C has no label.
 Volume Serial Number is BCCA-B4CC

 Directory of C:\test

2008-07-18  23:34       527,999,616 500MB.fixed
               1 File(s)    527,999,616 bytes
               0 Dir(s)   2,320,416,768 bytes free

C:\test>698472 -RECLEN=96 500MB.fixed
Took: 5.000000 seconds

C:\test>dir 500MB.fixed
 Volume in drive C has no label.
 Volume Serial Number is BCCA-B4CC

 Directory of C:\test

2008-07-18  23:37       527,999,520 500MB.fixed
               1 File(s)    527,999,520 bytes
               0 Dir(s)   2,320,445,440 bytes free
[download]

I'll grant you, it does have the virtue of simplicity.