Michael Fesser wrote:

My scripts make use of many of the new OOP features in PHP 5, so they won't run at all on PHP 4.

Ditto.

My current big pet project is http://demiblog.org/. This is PHP 5+ only and supports MySQL 5+ and PostgreSQL 8+. Although I do realise that earlier versions of these packages are still quite widely used out there, this project probably won't hit the big 1.0 for another year or two, by which time, the hosting world will have probably moved on a lot. Supporting older versions of PHP and the database engines will cost development time and push back the project release date even later, by which time PHP 4 support will be even less relevant.

So although PHP 4 may still be alive right now, it's counting down the days to his retirement when it can hand over the family business to his son PHP 5. He's heard the happy news that his dranddaughter PHP 6 is planning on following in their footsteps too as soon as she graduates. Because of PHP 4's impending retirements, he's not taking on any more big projects at work, and is letting his son take on most of the new clients.

Analogy over, it would be unwise at this point to look at supporting PHP 4 for any medium-to-large projects that are starting now or in the future. Existing PHP 4 projects should probably keep supporting PHP 4 for a while yet, but should certainly make an effort to support PHP 5 as well, and should be keeping a close eye on PHP 6 developments.