We are trying to recompile PHP5 on all of ours servers. It’s tough. You can’t know what errors would appear on your websites, and how severe would they be. I found some good articles about incompatibilities between PHP4 and PHP5 that I’d like to share.
http://www.php.net/manual/en/migration5.incompatible.php
http://www.faqts.com/knowledge_base/view.phtml/aid/22154/fid/1150
“Surely if there’s ever a time to hop onboard PHP5’s sublimely object-oriented and exception-handled bandwagon it’s during a ground up re-write?
The fact that php.net is still running PHP 4 is telling indeed. Haven’t managed to find any gossip as to why, perhaps someone knows something about this?”
http://www.sitepoint.com/blogs/2005/02/15/whats-keeping-you-from-php5/