First, congratultions on a good product.
Im writing a notificator for our internal chat (not Jabber).
I looked at http://www.jetbrains.net/confluence/display/TW/PluginDevelopment+ but this now seems to be out of date.
Then I looked at the Jabber notifier and that pointed me in the right direction.
Id really like to see some JavaDoc for jetbrains.buildServer.notification.Notificator but I cant find it. Im guessing I need to register the Notificator with the server.
Also, I cant find a useful feature that was in CruiseControl - 'first sucessful build after failure' - obviously this is useful so I dont spam with succeeding or failing builds.