And of course you can use Mason with Catalyst: http://search.cpan.org/perldoc?Catalyst::View::Mason
In this scope it's just another view like http://search.cpan.org/perldoc?Catalyst::View::TT , http://search.cpan.org/perldoc?Catalyst::View::XSLT or others http://search.cpan.org/search?query=Catalyst::View::
Mason is a really excellent templating system. I can't recommend it highly enough for that purpose.
(It is also handy for abstracting away mod_perl2, CGI, and FastCGI with a uniform interface.)
You'll see some names here of sites that use it that you'll recognize: http://www.masonhq.com/?MasonPoweredSites (Amazon.com being one of the most notable).