My company bought 3 3-year licenses for Zend Studio earlier this and up until a few weeks ago, there was nothing else on the market that even came close to meeting our requirements. Then Netbeans released 6.5 with PHP support. Right out of the gate, their PHP and JavaScript support is on the whole, so much better and faster than Zend's product, with so many fewer bugs, that despite the fact that we spent $1000 this year investing in Zend's product ... I am assisting my team in migrating over to use Netbeans for most of our development. There are a few things that Studio does better, but Netbeans is just a much more mature and easy to use product, even this early in their PHP support

http://blogs.sun.com/roumen/entry/is_netbeans_disrupting_the_php