The bare block around the grep is important... Change this line:

grep {$_ == 0 and $found = 1 and last} @middle;
[download]

To:

{ grep {$_ == 0 and $found = 1 and last} @middle; }
[download]

And I get:

Benchmark: timing 1000 iterations of foreach_middle, grep_middle, hash
+_middle...
foreach_middle:  1 wallclock secs ( 0.80 usr +  0.00 sys =  0.80 CPU) 
+@ 1250.00/s (n=1000)
grep_middle:  3 wallclock secs ( 3.09 usr +  0.00 sys =  3.09 CPU) @ 3
+23.62/s (n=1000)
hash_middle: 30 wallclock secs (26.40 usr +  0.02 sys = 26.42 CPU) @ 3
+7.85/s (n=1000)
[download]

-Blake