That's very interesting. That link is dead though.
One of the nicest AND most frustrating parts of taint-mode, for myself, is that once activated it remains on until the end of execution. It's not scoped, which removes some of the headache of using such a thing. Switch on, and assume always on.
http://example.com/upload.pl?file=../../../../etc/passwd
The main thing you had to remember was the parameters (all tainted of course) had to be filtered through a regular expression before you could use them.