I've used DWMX 2004 for a few months now. I can say that it is chock full of bugs. It uses some sort of scripting system, and if that errors it can cause a full crash of the application. The PHP support is pointless to say the least. The 'live' link is basically just an embedded browser. I would never write PHP with it, PHPEclipse is way better (as I'm sure is Zend Studio).
Having said all that, DWMX 2004 blows away the competition when it comes to building webpages. Fantastic control of HTML, CSS, Flash, file management, website management. It can do regular expression matching and replacing across a whole website (very very handy if you work with static sites). The local/remote ability is great for working between Windows and Unix (which I do every day). Also the Macromedia extension library is very good.
And to think I used to use Frontpage. Shudder.