The PHP development team is proud to announce the first alpha release (Windows binaries will appear in the next few days) of the upcoming minor version update of PHP. The new version PHP 5.3 is expected to improve stability and performance as well as add new language syntax and extensions. Several new features have already been documented in the official documentation, others are listed on the wiki in preparation of getting documented. Please also review the NEWS file.
Among the list of new features/improvements are things like namespaces, late static binding, lambda functions, closures, support for mysqlnd and removal of support for pre-Windows 2000 systems. For more information on when the full stable version will his the web, check out the release plan.