be a little late to join this discussion, but zwon's comment is most of what I wanna say, I would be more polite tho. jk ;)

Even as a multi-process model, perl5's ithreads is still not good enough. copying every thing to new thread/process is insane to me.(refer to this ) As a perl fan, I just hope perl would have some more weapons to compete

In short for threading thing, if you meet a scenario for heavy multi-threading, consider other languages(Erlang, GO like BrowserUk said) or XS other than pure perl.

UPDATE Fixed this link, Thank Happy-the-monk