I would rephrase that:

Especially in CGI scripts, ...

And I would add: Always do "perl -T -cw my_cgi_script" in a command-line shell before you make it runnable on a web server, to make sure it compiles with taint checks in effect.

(update: a lot of taint checks can only be applied at runtime, and I'm not sure I can identify any compile-time taint checks, but your cgi script should have "-T" in the shebang line, and when that's true, a shell command line like  perl -cw my_script won't work.)