As for garbage collection, there are serious arguments about whether Perl should do real garbage collection. So far it does not, but I suspect that Perl 6 will vary between implementations, and to my eyes that will be a very bad thing. Given the choice between truly reliable destruction semantics and cleaning up circular references, I know which one matters in my code...

As for your claim on having to rewrite the program when you hit a performance duh, my experience contradicts that. Of course you need to make an effort to modularize and an ongoing effort to clean up and organize your code-base, but then overall development goes faster, you wind up with less buggy software, and when you find the inevitable performance 'duh', you can generally fix it fairly easily.

Of course to get to that point you have to be willing to constantly pay the penalty of calling lots of small functions, loading modules, having some sort of centralized development system, and all sorts of other things that slow you down in the short term. I have seen (read had it demonstrated to me) how much this will speed you up in the end that I now firmly believe in putting ease of development and maintainance well above raw performance...