According to this new report on the W3 Techs site, the usage of PHP 5.2 has been passed up by the numbers for the usage of PHP 5.3 (finally).
PHP 5.3 has been released in June 2009, so it took a while to gain that level of popularity. End of support for PHP 5.2 has been declared in December 2010, but is was still the most popular version until now. Version 5.3 will enter the end-of-life cycle in March 2013. Version 5.4, used by only 3.0%, is now considered state-of-the-art.
The numbers have been consistently trending towards intersection with the usage of PHP 5.4 picking up, but no where near the 5.3 and 5.2 numbers. They also point out that PHP version adoption has a history of being slow. Contributing factors to this could be the overall impression of the language and how much "room for improvement" it seems to have.
It's not difficult to predict that PHP as a language will continue to dominate web development in the near future. What will be more exciting is to watch what new versions of PHP will look like.