in reply to use CGI or die, even with mod_perl?

You don't need CGI.pn unless you want to make your scripts backwards-compatible to CGI. You don't need Apache::Request either, since you can just use the args() method of the Apache object you get passed. Here is a simple example Apache::Registry script:
my $r = shift; %args = $r->args(); $r->send_http_header('text/html'); print "You said your name was " . $args{'name'};