Your list is interesting, because in my own case, your #2 (idioms, map, grep) came at #5, after everything else. I suppose that's because previous experience with C pointers made references easy, and experience with grep and awk did the same for regular expressions (though I agree that there's always more to learn about those). Also, you just can't do a lot of useful work without regexes, complex data structures, and CPAN.
You can get away without map/grep and other Perlish methods like statement modifiers, though, by using a lot of loops and making your code look like C or some other language. So I tend to think of the idiomatic stuff as the sign that someone's not just capable of programming in Perl, but comfortable with it.
I suppose everyone's list might be a little different, based on their own previous experience.
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