If you're a Java programmer and interested in adding sexy Ajax goodness to your apps, a good starting point is Matt Raible's presentations, which he has made available for download for those of us who can't actually go see him talk.

update: The pdf presentation I downloaded actually doesn't seem that useful on its own, it doesn't contain as much information as I'd hoped. Most of the slides are just Matt's photos, that I assume illustrate personal ancecdotes that he uses to make points about the topic, but are kind of baffling on their own. I think the equinox-ajax.zip file probably contains code examples, but in the past when I've downloaded Matt's appfuse framework starter kit I couldn't really get into it, and I believe equinox is a version of that. Bram Smeets intro to using DWR may be a better start.