I guess you are using Perl 5.005 and not Perl 5.6... This (poor) obfuscation makes use of the 0b form which allows you (in Perl 5.6) to use binary numbers as you use octal or hexadecimal ones.

I voted it --, because... well, I didn't have to run it (I don't have Perl 5.6 installed here, anyway) to clearly understand what it did.

Here is some Perl/Lisp, done by stefp, in the course of Paris.pm $A++ contest:

; q
(setq A (if (boundp 'A) (+ 1 A) 1) ) ; $A++;
[download]

Not a tough nut to crack, but hey...