I've been waiting a while to drop PHP 4 and move completely to PHP 5 for the projects I'm involved with but there is a problem with getting hosting companies to upgrade or to provide the means to switch between PHP 4 and PHP 5.
I understand the problems involved with such an upgrade, but I also get the feeling that many hosting companies have been putting this off for as long as they possibly can. This has created a bit of a stalemate where PHP developers don't want to commit to PHP 5 and the self-depreciating cycle continues.
To help move this along, the GoPHP5.org website was created to promote the move to PHP 5 by listing projects that have agreed to cease support of PHP 4 by the February 6th 2008 deadline. The site does a very good job explaining the issues involved.
In addition, a couple of weeks ago, the official PHP website announced that PHP 4 has reached the end of its life and that support will continue only through to the end of 2007:
Today it is exactly three years ago since PHP 5 has been released. In those three years it has seen many improvements over PHP 4. PHP 5 is fast, stable & production-ready and as PHP 6 is on the way, PHP 4 will be discontinued.
There are many reasons to move to PHP 5. For me, the revised object model is what I've been waiting to use fully - it now seems like the ideal time to upgrade.