As Lukas Smith mentions, the latest alpha release for the PHP 5.3 series has been released - PHP 5.3alpha2.

Wow, after what feels like ages PHP 5.3.0alpha3 was just released. Originally we hoped to be able to release now intermediate releases every 2-3 weeks, this one took a good 2 months. Somehow this releases did its very best to stall itself. People that needed to work on things together by chance ended up being busy with other things and vacations in just the right order to make things impossible. Most of this was to be attributed to the namespace discussions, which climaxed in the backslash FUD campaign.

He notes that a stable release is probably looking good in Q1 of 2009 (with namespaces being the delaying factor). He also suggests something that could help make things a bit simpler in the future - making the internals@ mailing list read-only for anyone outside of core developers. A good bit of the confusion and bickering came from those outside the dev team and it didn't help the group come to a decision any earlier.

You can find the official release information for the alpha2 on the main PHP.net website.