Good start: don’t use it unless you need to, there’s plenty of alternatives, e.g. DOMXML, str_replace, etc. Also PHP5+ has lots of filters for email validation and URL validation etc, function calls you can make rather than complex regular expressions. Regular expressions can slow down quickly due to back tracking, pattern complexity and long strings.
Then the talk has become abstract, each point is prefixed with an odd statement such as “Only elephants remember everything” and “Not all matches are made in heaven” – people are getting it, but everything needs explaining before they get it!
One very good point I have seen ignored many times is “try not to be greedy.” For example /<(.+)>/ in the string <a href=””>fdsfsd</a> will match the entire thing. To make it ungreedy, either use /<(.+?)>/ or /<([^>]+)/ . Greedy matches can be 20+ times slower.