A quick tip:
If you're developing an iChat service plugin with IMServicePlugin and friends, don't forget to run this from the command line after you install the plugin:
killall imagent
It appears that in order to actually get your plugin to load, imagent needs to be restarted, and restarting iChat itself isn't quite enough. It doesn't look like you need admin privileges to kill imagent so 'sudo' isn't necessary. This also makes it easy to do as part of your build process - just add it to a script that runs after your build.
If you don't do this after you install new service plugins, iChat will see your plugin (and list it in its services list) but won't actually load the plugin itself.