There's nothing more telling about the quality of a conference than a personal experience and the Zend Developer Zone has posted one from Jason Austin and Garrison Locke about the ZendCon conference they attended back in 2006 and some of their experiences there.
One day when browsing around the internet Jason came across a posting about the 2006 Zend Conference being held in November. It was billed as "the premiere PHP conference." We asked our manager if there was any way we could attend. If we were going to be "real" PHP developers, we felt like we needed to be at this event '" it was the definitive place to be if you were in the PHP world.
They talk about the reality check they got when attending the conference - learning things they'd never heard of before ("fantastic and intensely frightening") in talks like Matthew Weier O'Phinney and Mike Naberenzy's "Best Practices for PHP Development" session.
The article's a good read for anyone considering attending a conference, either ZendCon or any others through out the year.