There's a new Oreilly book out on it called 'visualizing data'.
I'm only a few chapters in, but it's quite good so far. Covers the basics, a few good sized 'real' projects, and quite a bit on integrating it with java.
I've had great experiences using processing.
It's been sweet for prototyping multimedia stuff - live video processing, physical computing, data visualization, toys.
The libraries make it quick and painless to get graphics floating around.
I've been involved with the project off and on for a few years now. (I wrote the Interfascia GUI library for Processing.) As an interface designer, I find that it makes a great tool for rapid prototyping.
I don't have anything specific to share, but my past experiences were pretty good. It's definitely great for doing toy types of things (I wrote a 3d clock, for instance, that changed color based on where the hands were). There's also great library support and a pretty big community. If I happen to dig up that clock I'll post it.
I have nothing to share, but check out this site it has a bunch of different processing stuff, http://createdigitalmotion.com/tag/processingorg/ the best site is their site and the forums, just cruise them and you'll find all sorts of good stuff
I'm only a few chapters in, but it's quite good so far. Covers the basics, a few good sized 'real' projects, and quite a bit on integrating it with java.