Dealing with large web based applications with multiple forms is a minefield.
It's often hard enough to ensure you validate all your input at all, without
having to worry about doing it in a consistent manner. If any of the validation
rules change, you often have to alter them in many different places. And, if
you want to operate taint-safe, then you're just adding even more headaches.

WWW: http://search.cpan.org/dist/CGI-Untaint/