I would say Perl 5.0 was major (objects). Somewhere in the 5.8 (unicode) series was major, and 5.10 was less major (ithreads). I personally use 5.10 as my "old" Perl to test with, and code to 5.10 or 5.8 or even accidentally older. 5.6 and some of the 5.8s I consider a totally different generation than todays. In the 5.8 series, major changes were done in the minor version numbers, unlike today.