The basic format seems good. I'm not sure about using weak_ref, though -- what if an object or structure falls out of scope, yet there's still a key in the data registry? If another ref comes along whose fingerprint matches that key, does it end up getting replaced with undef ? (I'm kind of sleepy at the moment, so I could be misreading the code).
Also, as originally implemented in the context of DateTime::TimeZone, I was using class structures and class methods. You've moved it into object mode, which is fine, but I'm curious as to how you utilize the shared object. I'm assuming it's a single object in the DT::TZ base class? Cheers, Matt
