I have been using Eclipse for some time now and it's the first IDE that I can compare to Visual Studio 2005. In some respects I'd say it's better than VS, but then I use them for different languages. I like the fact that Eclipse is multi-platform and free (as in open source).
One of the best things about Eclipse is that it is easily pluggable and has as a result lots of great plug-ins. I've been using the EasyEclipse Expert Java distribution with some of the EasyEclipse plug-ins, one of which is PHP Eclipse.
I've heard some people speak of not using Eclipse because it's Java and "Slow". Now I don't have a fast computer (laptops are expensive things), but I'd have to say Eclipse is very responsive, way more so than VS.
Java and Eclipse
I found one site that is great for beginners of both Eclipse and Java. Dave Powell at Elon University has created a great video tutorial on everything from setting up Eclipse, debugging and GUI programming to unit testing in Java using Eclipse.
Experience with CakePHP and Eclipse
CakePHP is a rapid application development toolkit for PHP centered around the Model-View-Controller pattern. I've found it by way of searching for a PHP alternative to Ruby-On-Rails (as rails hosting is still harder to come by).
Maybe I just don't know how, but I could not seem to make Eclipse use the correct coloring or syntax-helpers with the default .thtml view file suffix. I've solved this for now by using .phtml and in the controller set $this->ext = '.phtml';. After that Eclipse has been very comfortable to work with.
Im using EasyPHP as my LAMP server.