Recently PHP.net announced, with their latest PHP 5.2.14 release, the end of active development of the PHP 5.2 branch. End of active development means that there will be no more new features or bug-fixes released in the current 5.2 version, and users are encouraged to move to the latest 5.3 branch of PHP. However, security updates will be considered on a case-by-case basis.
According to a recent Twitter poll, we found that over 50% of developers are already working with the latest 5.3 release. An additional 35% is already in the process of migrating to 5.3. This means that the majority of developers see the importance of upgrading and are already taking action, well before PHP's announcement. (We are aware, though, that we are surrounded by a particularly well-educated group of hard-core community people, so these results might be slightly skewed.)