Led, not surprisingly by Zend (the best known commercial developer of PHP tooling), the Eclipse PHP project covers a subset of what Zend offers in its IDE, Zend Studio. PDT 1.0 includes context-sensitive editors that provide syntax highlighting, code assist, and code folding (which abbreviates pieces of code that are not being worked on). It also provides support of incremental debugging of PHP code.
In essence, this is a subset of what Zend already provides in its IDE. But the key is that it provides a way for PHP developers to tap into other goodies from Eclipse, such as the Myelyn task manager.
