The Hackathon was a lot of fun. Pamela Fox, one of the developers of Wave, gave a couple of presentations (1, 2).
There are some article on debugging Wave extensions for Robots and Gadgets. More handy debug tips here.
If you're writing a Robot in Java, a huge amount of support is available in Google's Eclipse plugins. Be sure to have Java 1.6 installed. If you already have an earlier version, you can install 1.6 on top of it, and just switch the preference within Eclipse. I think it was Windows -> Preferences -> Java -> something...
There is also an Eclipse plugin for Python called PyDev. I don't have a lot of experience with it.
One guy at the Hackathon wrote a robot in Groovy, a dynamic language that runs on the JVM. From what I could tell, it was working fine.
At the present time, Robots must be deployed to Google App Engine. This restriction will probably be relaxed, especially as non-Google Wave servers come on line.
App Engine doesn't run PHP (I had wanted to add Mediawiki to my web app) but if you really want PHP you can try Quercus.
App Engine has a great logging facility, accessible via https://appengine.google.com. You can put logging statements in Python code (import logging) or Java code (import java.util.logging) and both will dump info statements into the GAE log.
Google likes extensions to adhere to some design principles. These are designed to maximize the broad appeal of your Wave extension and to make it run faster. Google figures that slow ugly extensions will drive users away from their ads.
There was talk at the Hackathon (and I wasn't paying close enough attention) about people setting up Wave servers. If I set up my own server, can I issue my own invitations to people so that I'm not depending on Google providing invitations? That would rock.
More useful links:
- http://wavecompass.net/ -- a mediawiki that tries to fill in gaps in Google's Wave docs
- http://www.reddit.com/r/wave -- random semi-useful Wave discussions on Reddit
- http://code.google.com/p/pygowave-server/ -- a Wave server in Python
- http://code.google.com/p/wave-protocol/ -- the official Google wave server in Java
- http://completewaveguide.com/ -- Gina Trapani's Complete Guide to Google Wave is fantastic