You claim that forks duplicate everything? I think not. At least not on any OS which implements copy on write memory, which would be any semi-current *nix. And in many applications it is OK if communication overhead is slightly more in order to benefit from the saved memory and increased protection.
As for the rest, I haven't tracked to see if people's experience with Perl's threading in the last half year is as bad as it had been before that. It probably has improved, though not to the point where I'd be willing to put it into production. But my general comments about threading remain true, and my specific comments about Perl's thread model in specific are, to the best of my knowledge, accurate. If you have specific examples to change my mind, that would be one thing. But you don't appear to, instead you're just telling me that what I've said is red herrings and wrong, without providing me with any specifics.
Since I feel no need to convince you of anything, and I don't feel that this conversation is going anywhere I'm exiting the conversation here.