I've been using Zend Studio pretty regularly since September and I won't give it up now
The automatic syntax checking, and bracket highlighting are 2 things that have saved me quite a few hours of looking at code.
Another thing I use it for is testing theories with code snippets. I write a section of code, and do some dummy valuse, and watch the output and variables to see if it behaves like it should.
It also has integrated CVS support, and other things.
Zend may seem expensive at $199 ($249 w/ support), but NuSphere PHPed is $299 ($499 with support).
If you are looking for a free editor,
www.winsyntax.com is where to go. It's lightweight, and does syntax checking.
