Mike Potter has posted an update to his blog about the unofficial Adobe PHP SDK he mentioned earlier with details about new information and corrections that have been added to the guide.

I've updated the (unofficial) Adobe PHP SDK to fix some problems after the initial release. Turns out a few files were missing from the .zip file, and some files were misnamed. I've fixed these problems and also added in a new, more simple sample to show how Flex can retrieve XML data from a PHP backend, without requiring the use of a MySQL database. Finally, I've also removed the .svn files from the .zip file, reducing its size to only 1.5 MB.

You can download this latest version of the guide directly from his blog as well as get involved via the Google Group or requesting access to the SVN repository on Google as well.