Having somehow avoided much Perl for most of my working life, I've recently done quite a bit of it (Perl 5 this is), and I have found it, syntactically, a painful experience when compared to Ruby and Python. The one thing I have loved compared to those two though is the performance. If Perl 6 retains that performance edge it may gather mindshare, but otoh my impression of Perlists that I work with is that they are quite content with Perl 5's warts, so I am not convinced that 6 will have much of an impact.
If I have one piece of advice for people coming from other languages into Perl 5, it's to not be fooled by some similar looking syntax into thinking it should be used like C or any other C-like language. I find assumptions in that vein are often what leads people to painful assumptions about the language.
If I had time for a second piece of advice, it would to be sure you understand context in Perl 5[1]. Everything is based around context, and to not be aware of how it factors in to the current expression often leads to befuddlement (at best) or anger. On the flip side, context is often where Perl shines. I recommend Chromatic's excellent Modern Perl: The Book[1] if you feel any of this might apply to you.
Finally, Perl can be a very Lispy language. Avoiding those parts (map, grep, etc) is sort of like consciously avoiding every even gear when driving a car. Possible, but much more painful than using it as designed.
Edit: Oh, you probably want that reference I implied up above.
