Niall Kennedy 
points to a 
presentation about Flickr and PHP given by 
Cal Henderson of 
Ludicorp.  I'm pleased about this, because Cal used a screenshot of my Flickr Rainbow as an example of Flickr API usage.  The rainbow is down at the moment, but a new version is coming soon.  Exciting additions will include respect for Creative Commons licenses (only photos licensed for derivative works will be used) and a standalone non-applet version (I might even do a continuously updating screensaver version, one day).