MTA publishing (php|architect) has released another new book - Stefan Priebsch's "Guide to PHP 5 Migration":

Written by Stefan Priebsch, this is the only book you will need to help you through the rough spots when migrating your PHP apps from PHP4 to PHP5. Not only is this an extremely comprehensive and in-depth resource, it will show you virtually every pitfall you may encounter and will undoubtedly make your migration as smooth as possible.

The book covers things like the concepts surrounding migration, some strategies to follow and an outline of a recommended migration process (as well as some tools to help). You can find out more about this new book on its page on the php|architect website and order your own copy - $33 CAD for the print and PDF versions together and just $29 CAD for the PDF only.