The Future of IM

Just had an idea while reading this post on Jamie Fristroms Blog where he explains why he is using his instant messenger as little as possible. His concern is that his contacts may be offended when he is online but doesn't talk to them, or that they want chat with him while he is working so he doesn't get anything done.

"I'd suddenly find myself in the grave after having wasted my life IMing people."

In the comments Joel recommended to use different accounts for different contexts but my idea goes a bit further. What if the instant messenger itself supported contexts?
Every contact could be associated with one or more contexts so they would only see you if you were in the same context, as shown in this image:

Switching between different contexts would be as easy as changing the status from "online" to "away" but would help immensely to keep your friends from distracting you.
A further idea is to block messages from other contexts so you can only communicate with contacts in your current context, this would help to keep all those out who try to send you offline messages in the hope that you are only invisible. :) (And yes, the messages should probably not be discarded, just hidden until you are in the correct context.)