I find Quanta plus, part of KDE Web Development very useful indeed. Its a good balance between overpowering IDE (like eclipse) and useful editor methinks.

Personally I'm a fan of editplus, it's small, fast, syntax highlighting, ftp support are fantastic.

What are the advantages of using a full IDE?

Personally I find autocomplete extremely distracting.

Projects are supported by editplus, but then again why would I want 50+ files open at once?

I can set up the php manual CHM to bind to CTRL+1 so I can quickly find a function (I can even highlight a function name like strpos and hit CTRL+1 to automatically display it).

In the end it's all about personal preference. Those features I find annoying others will like. That's why there are so many choices / options available.

If mouse is your case, then use notepad. And if you're into large scale web applications with clean OOP, Zend IDE is the only best solution.