View Triggers

It seems that insertion triggers on views will/may be added in version 8.3.
http://archives.postgresql.org/pgsql-general/2007-02/msg01466.php

However, Tom mentioned that adding update and deletion triggers may be a bad idea:
http://archives.postgresql.org/pgsql-general/2007-02/msg01466.php
...
However, I'm not sure that the idea scales to cover updates and
deletes; with no concept of physical tuple identity (ctid) for the view
rows, it's not clear that you can write triggers that will reliably do
the right things.
...

I am curious about the dangers could occur if UPDATE triggers were implemented on a view? I
assume that these dangers are most apparent with views that are based upon joined tables rather
than views on a single table.

Do these dangers also apply to update DO INSTEAD rules?

Could there exist any view design guidelines that if followed would allow for the safe utilization
of update triggers?

Regards,
Richard Broersma Jr.