Google Talk now has a chat bot called Guru that will answer your questions - but don't get too excited for a guru it doesn't understand much and could do better.
Google Talk Guru is a simple bot that lets you ask questions using Google Talk. You can phrase your questions in a fairly natural sort of English and Google's search engine and other servers will attempt to find an answer for you .
You can ask questions like "What is the weather in New York" by sending this as a message to firstname.lastname@example.org. If everything is working you should get a weather report back as the next message. Google give examples of questions on sport scores, weather, calculations, definitions, currency, language translation and web pages. It isn't clear if this is a complete list or not but if you test it you will soon find that it is fairly limited.
This is not Google's challenge to Wolfram's Alpha, say. In fact given the language skills Google has managed to master it is something of a non-event. The language processing back at the server can't be much more than a simple matching algorithm with a link to Google search and translate. When you compare its performance to the average chat bot it really doesn't seem to be trying.
Of course Google Talk isn't the most popular IM service overall - that's either Live Messenger or Skype depending who's stats you believe - but Google Talk is on all Android phones and this does give it a niche advantage. Until Google Talk's Guru you could perform a search via SMS, but with most Android phone users having a data plan this doesn't seem a good way to work. The same argument holds for Guru of course. It might be lightweight but unless it can perform better than it does at the moment most users are going to power up a mobile browser to get their answers.
The basic idea is a good one but Google Research needs to set itself some more ambitious targets in the near future or Guru isn't going to have many chats.