The PHP development team recently introduced the latest version of the new PHP 5.3 branch, PHP 5.3.1. This version essentially does not change the essential core 5.3 PHP engine, but by focusing on stability and security, the PHP team has introduced more than 100 bug fixes and tweaks to the overall framework.
Something that I find very encouraging is the PHP team's very conscious drive to empower the security features of PHP. There was a time not so long ago when PHP was considered rather unsafe for commercial purposes, but now I think that sentiment is changing and the world is becoming open to the power of PHP, as well as it's usefulness.

The most significant and security-conscious addition in PHP 5.3.1 is the inclusion of a max_file_uploads INI directive, making it possible to limit file uploads per request to 20 files by default. This is extremely important in circumventing denial of service (DoS) attacks.

If you have not heard of denial of service attacks, the basic principle is that a website gets pounded with hundreds or even thousands of requests at the same time, thus rendering the server essentially useless because all of its sources are being consumed in serving the attack. Thus, a user having unlimited upload possibilities certainly could bring a production server to its knees by constantly uploading something like one hundred files repeatedly from various machines. You could in effect have 1000 or more files being uploaded at the same time, and a slow or shared server will not handle that well at all. Even a dedicated server would struggle considerably. So, what max_file_uploads does is make sure that no more than 20 files can be uploaded at a time on that server.