I recently had the pleasure of updating a server to PHP5 from PHP4. Having upgraded a few before without any hassle was leaving me with an impression that the conversion might actually be smooth enough to finally take the step and upgrade from PHP4 to PHP5.
As fate would have it, this server turned into a nightmare of errors, mostly isolated to a few illogical, yet valid, PHP4 usages of in_array() – however it left a flood of errors all over the website running on the server.
So I took a step backwards in my effort to try and upgrade from PHP4 to PHP5, which is a shame – since allow_url_include would make my day so much easier.
The only advice I can think of, is enable error logging to a file on any server you upgrade, to catch those errors as soon as possible.
Although many think the lack of adoption of PHP5 is related to CMS systems and other open-source projects not being fully compatible with PHP5 – fact is, what’s stopping the adoption is Avarage Joe’s code.