To see your program as Perl sees it, deparse it:

c:\@Work\Perl\monks>perl -wMstrict -MO=Deparse,-p -e
"print 'Enter decimal number less than 256: ';
 my $decimal;
 $decimal=<STDIN>;
 chomp $decimal;
 print $decimal & 128 <=> 0;
 print $decimal &  64 <=> 0;
 print $decimal &  32 <=> 0;
 print $decimal &  16 <=> 0;
 print $decimal &   8 <=> 0;
 print $decimal &   4 <=> 0;
 print $decimal &   2 <=> 0;
 print $decimal &   1 <=> 0;
"
BEGIN { $^W = 1; }
use strict 'refs';
print('Enter decimal number less than 256: ');
my($decimal);
($decimal = <STDIN>);
chomp($decimal);
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
print(($decimal & 1));
-e syntax OK
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See O and B::Deparse.

Update: Why does every expression like  128 <=> 0 become the constant 1? Because the Perl compiler, like most compilers today, is smart enough to know that the result of the comparison of a constant to a constant is just going to be yet another constant, 1 in all these cases. (Update: I believe this process is called constant folding.)