I've been running Zend since 2.6 came out for Mac OS X an d I've got to say it's saved me tons of time. The current application I'm working on has over 60 classes. Zend includes all the methods for those classes in the code completion library. Major time saver! If I was doing alot of in-line development I don't know that Zend would be any better than using Dreamweaver (not the modules) or BBEdit but as an OO coder Zend is a life saver.
On the downside there are still some OSX integration issues, mostly with key bindings being hard coded instead of use the key mask. This means some commands work with Apple+key and some still use the windows Control+key. Also I've had problems with project not loading properlly on start up.. but that's only on the work machine where my home directory is on the network server.
Zend has come a long way. I highly recommend it for anybody building large scale php applications.