Chat bots can be fun or useful, but until now, deploying and maintaining a chat bot for Google Talk was difficult. Google has announced a new XMPP API that makes it easier to build your own chat bots with the Google App Engine.
The XMPP support lets you create apps that exchange messages with users on any XMPP system, including of course Google Talk, but any Jabber network. Where it gets really interesting is the built-in XMPP support for the fast-approaching Google Wave, which will be rolling out to a larger beta group at the end of September. This means that you'll be able to use the XMPP API to build bots that interact with your Waves.
For all the details, read the API release notes.