The rumours are true. Google has just released an IM service called Google Talk. Unfortunately, their client is PC only (like all the other Google software it seems). However, it seems that Linux and Mac users can connect to the Google Talk client as it uses the Jabber/XMPP protocol.
Update: At least one source is speculating that Google’s move is less about IM, and more about Google’s ambitions for Skype. Interesting.
Update 2: Interesting timing … Skype seems to have just released the SkypeNet API which would “enable developers to access our IM and Presence system and bring it into new applications without needing to have the full version of Skype running on the machine.”