I consider myself an Open Source Developer but I very rarely develop for the open source community. I create apps for businesses, where I work, and some side projects. I share code with those I work with obviously, but generally not with the PHP community as a whole. I share some items on this site that I think are helpful to people.
I'm not sure yet where I stand on the goPHP5 movement. I tend to use PHP5 on my newer development but still have to use PHP4 for legacy stuff. And by "legacy," I'm talking internet time here, so about 4 years is "legacy."
I'd like most of the common PHP apps to move to PHP5. I've got some PHP5 Wordpress plugins in my code repo right now. And heaven knows that Drupal could really use PHP5 (or even the namespace support in PHP6). But I think forcing their hand is a little harsh.
Photo Matt isn't moving Wordpress towards a PHP5 model any time soon. And this is a bummer. But I understand the point of not leaving users of your product in the dust. I don't really have that problem with my code.
As for my opinion, I feel like learning PHP5 was one of the best things I've done in my career. It helped the other object-oriented languages like Java and C# to seep into my head a little bit more. Knowing more then one language is always a good thing.
I love the object model in PHP5, as well as PDO, and the JSON extension is nice. But I find that I use the improved DOM handling of XML in PHP5 the most. It still really shocks me that more people aren't interested in using this. And it still shocks me that more people aren't interested in using XSLT and PHP.