in reply to mod_perl v. mod_perl 2

http://modperl2book.org/
As with any major upgrade, there are new features and key changes to mod_perl from the 1.x generation. The mod_perl 2 User's Guide explains these key changes and demonstrates the tools that you can use to port modules and migrate your existing code. Improvements in Apache 2 and mod_perl 2 include:

http://perlbuzz.com/2007/09/interview-with-jim-brandt-coauthor-of-mod-perl-2-u.html
Andy: You say that mod_perl 2 is the future, but what if I've got a perfectly good, working stable app running under Apache 1 and mod_perl 1. Staying on mod_perl 1 is certainly building up technical debt, but what does mod_perl 2 give me for my troubles? ...