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.

The PHP development team would like to announce the immediate availability of PHP 5.3.3. This release focuses on improving the stability and security of the PHP 5.3.x branch with over 100 bug fixes, some of which are security related. All users are encouraged to upgrade to this release. [...] The PHP development team would like to announce the immediate availability of PHP 5.2.14. This release focuses on improving the stability of the PHP 5.2.x branch with over 60 bug fixes, some of which are security related.

The announcements list some of the major security enhancements and fixes in both new versions as well as a few new features like updates to the PCRE libraries and more.

Note: this PHP 5.2.14 release marks the end of active support for the PHP 5.2.x branch. It is encouraged that you upgrade to PHP 5.3 by following the steps in this migration guide.

I can't say the results of the benchmarks are surprising, but it does give a good idea of where, speed-wise, they really improved things in this new release. There are some stats, though, that didn't make that much of a jump. Those seem to be ones dealing with objects and their handling, though - so there's not that much of a jump there anyway.

He tested all sorts of operations, including working with binary data, string and array functionality, looping (for, foreach, etc), and operators. For each statistic, he provides what the test is doing and what the results are. Testing was done with the PHPLens benchmark suite.