David Coallier has some happy news for PHP developers all over - namespaces have officially been committed to to HEAD branch:

This means that the next PHP version (5.3) will have namespaces. The patch by Greg Beaver to allow multiple namespaces has not been applied yet but I sure do expect it to be applied to 5_3 and HEAD soon.

More technical details can be found via the patch details and some basic articles on how to use them in your code.