I've done a few presentations previously: there's a reasonably complete list at http://jon.oxer.com.au/talks. I've talked at Melbourne PHP User Group, LUV, LCA, LinuxTag, OSDC, Debian Miniconf, Contracts On Show, Swinburne University, CeBIT, Google, and a number of business networks including Business Boroondara and Rotary.
This particular talk has been delivered in various incarnations three times, including at Open Source Developers Club in Melbourne in late 2005, as the opening keynote of Open Source Developers Conference in Melbourne in December 2005, and at OSCON in Oregon in July 2006. The talk has been further developed each time with new techniques demonstrated, and for many attendees it turned out to be the unexpected smash-hit of OSCON. Comments from a couple of attendees can be seen at:
Even those who saw a previous version of the talk at OSDC would have a lot of updated content to see.