Most of them would have moved onto Perl web frameworks. Rough timeline would be:

    Perl --> cgi
         \--> mod_perl
          \--> Mason
           \--> CGI::Application
            \--> Maypole --> Catalyst
                         \--> Jifty
                          \--> Mojolicious
                           \--> Dancer
                            \--> Squatting
                  \--> Continuity         
                   \--> PSGI / Plack [works with all the above]