As mentioned by Richard Heyes, there's a new blog post from Larry Garfield talking about the death of PHP4, how the community has responded to it and some of his own thoughts on the matter.

The problem is the source for that "everyone" [is still using PHP4] claim. The most widely referenced stats are the Nexen stats, and according to them 70%+ of the world still uses PHP 4. Horrors!

He takes a closer look at the stats and comes up with a slightly different sort of conclusion that the stats can't really measure. They can show the server-based usage measurements of PHP4 vs PHP5, but they can't show the number of developers behind each of them.

According to Larry:

Even if we assume that 70% of PHP developers are using 70% of random servers running PHP, and that they're all using proprietary, one-off applications on a server with a sysadmin who refuses to upgrade at a company that has no support contract with any distribution vendor... Where are they?