Oh, obviously.
The performance improvements in PHP 5 are well documented. If you feel like you and your customers wouldn’t benefit from that, perhaps you need to rethink the service business?

Sorry for the cliché, but it’s the truth here. However, when we need to do some extra coding or whatever, we generally then rather do it in PHP 5 – but the old stuff can stay as it is, it’s working fine.

Obviously, I’m all for upgrading etc. and development, but here it’s just not really worth it right now.

I suggest switching your project to PHP 5 now. There are only a handful of actual, code-breaking incompatibilities between PHP 4 and PHP 5 — you do not have to write in E_STRICT-compliance to get code running on PHP 5.

Switch now, troubleshoot the little things like array_merge() usage and the other things described here:

http://www.php.net/manual/en/migration5.incompatible.php

… and don’t look back.

Then again I know a lot of users still running Windows 2k instead of XP (much less Vista) or OS X 10.2.x or 10.3.x though 10.4.x has been out for quite some time…

This can go on and on… why are the officially supported versions of apache for control panels like cPanel for hosting companies still based on apache 1.3.x code, and usually ship as well with php 4.x? In many cases the reason hosting companies have not upgraded many of these is simply the control panel companies so many base their management on are behind the times as well…

Not always an issue with the hosting companies or IT staff, it simply could be the selection of OS or management products that are still shipping older versions for stability or unknown reasons as well. Always easy to say “why don’t you” if you don’t manage 100’s or 1,000’s of servers, and 10’s or hundreds of thousands of clients accounts … breaking a single user is an oops if they are running older code, forcing 10’s or 100’s of thousands of users to possible break their web sites all at once if they are running code that does not work on php 5 is a great way to go out of business

1) Dog-bytes-tails problem:
- ISP does not upgrade
- coder of shrinkwrap php sw needs to still cater to users stuck on old platform
- ISP is not compelled to upgrade since apps keep running on php4
- etc..

2) php 5 was not really stable until 5.1.X (and not the first point releases). Plus minor api changes in-between 5.X

3) way too many small changes not really necessary but impacting your code (eg. making var deprecated instead of assimilating it to public, deprecating is_a, functions returning class/function names now respect case, curlinfo spits array instead of string, etc…)

4) not really huge gains for existing codebases (which will probably make usage of php libraries for doing json, xmlrpc, soap and the like)

I’ve used PHP 5 in production environments since it was beta (yes, beta), but now I work at a company that is PHP 4 and migration is not a snap: we have millions of users spread across over a hundred machines in an environment that works and there are not enough reliable acceptance tests to make this simply flipping a switch somewhere.

Migration is easy when you have provable large performance, development or feature gains. PHP 5 doesn’t do that for some of us. It honestly doesn’t. Assuming we get the bugs worked out, we could maybe improve the efficiency of our site by 20% with the improved object model and the availability of extensions for xml parsing, JSON, and memcache. Maybe if our site used XML more…

Those of us old enough to remember the PHP 3 to PHP 4 migration remember that it took a very long time (I switched our commercial site from PHP 4 at the end of 2000, but most sites were using PHP 3 for years afterward) and unlike PHP4, that offered real performance gains (Zend Engine vs. run-time) and features (object orientation, more extensions, etc.) with less compatibility headaches at a time when sites weren’t making tens of thousands to millions of dollars a day.

So migration for us will be tough and will involve me working extra hours in my spare time. I’m down with that. There are bigger rocks for to deal with during the day.

PHP 6 has the right idea: break backward compatibility and those who need features like i18n, APC, etc. will do the work to upgrade. The rest of the world can use PHP 5 or even 4.

And from that perspective, migrating to PHP 5 from PHP 4 makes a baby step to PHP 6.

-terry