Jonas Lindberg quoted,
With this feature, you can appear offline, and still send and receive messages. If you’re using AIM in Gmail, invisible mode also makes you appear signed out on the AIM network.
Many developers will find this interesting as they can chat with other fellow developers without any interruption now. One bad new for boys is that all gals can go invisible now to avoid them!
Personally this is the feature I was waiting for. Hope to see it in Google Talk application soon!