The first perl I used was some version 4. Later, I found out that 5 already existed at that point, which was why many things that I read about did work on my computer, but not on the web server I was using.

So I have experienced a transition from 4 to 5, and I have to say I couldn't live without references, lexicals and OO anymore. That's one of the major reasons I can't cope with PHP: it lacks real references and lexical variables.

The upgrade to 5.6 was great in many other ways. Lexical filehandles, lexical warnings, the our operator (lexical declaration of global variables), 3-arg open, 0binary notation, I like and use them all. This does mean my code is not compatible with the occasional 5.005 out there, but it makes everything a lot easier to create and maintain.

Upgrading to 5.8 was less spectacular. The only thing that comes to mind is that it has much better unicode support.

5.10 will shine again, with the introduction of the defined-or operator as the (for me) most important improvement.

I have used perl 1, and have even tried (for fun) to create Perl 1+4+5 compatible programs. It's possible! During this I learned a lot about Perl's history. See for example the archaic do syntax for calling subroutines, that is still supported in Perl 5!