As a devil's advocate and ignoring problems with PERLLIB and PERL5LIB, in a CGI enviroment I can do many things before I read any input from the user. So as long as taint is enabled by the time I read input from the user then the dangerous data is taken care of. There are only so many sources of input to control and it is an easy process to mark untainted items as tainted.
Thanks for your response. ++ to you.