in reply to Secret Perl Operators: the boolean list squash operator, x!!
I've said this once before. Using boolean algebra in numerical context relies on obscure implementation details while using the ternary operator relies on well-defined (and documented), designed-that-way implementation details. For that reason alone, I would not want to see this construct (not operator) in code I'd have to maintain later.
By declaring this an operator, you're making an analogy that it has some sort of precedence that can be used to avoid parenthesis - in fact, this looks more like a function in reverse (the parentheses come before the "name" of the function, which is "x!!"). So that makes it the first awkward operator we've got, even given all the extras (e.g., goatse operator, etc.).
I would instead suggest that a clearer, more maintainable version might be ($string) x ($cond ? 1 : 0). Definitely longer than your operator, but I'm not only not claiming this to be an operator (more of an idiom or pattern), but it'll be way more obvious to anyone reading it what I'm trying to do. Sure, there's still some duplication (the ?1:0 part), but not a lot more than the duplication your operator has (the x!! part).
That said, I don't find either of your original "problem" examples to be particularly onerous, and thus I may not be really appreciative of the elegance gained with some slightly obfuscated code.