I think IRC does half or more of this. Usually there are channels for specific things with a lot of varied experience and expertise. For instance in the #xml channel on Freenode, some very heavy hitters in the XML world frequent the channel. It also allows you to contribute back for the more basic questions that might get asked.
I like the personal contact in the abstract but it suffers from huge latency (have to wait a long time for an event and my questions probably don't last that long), and doesn't scale across domains e.g. In the #drools channel, I can talk to the guy that implemented the Defeasible logic decision plugin.
I like the personal contact in the abstract but it suffers from huge latency (have to wait a long time for an event and my questions probably don't last that long), and doesn't scale across domains e.g. In the #drools channel, I can talk to the guy that implemented the Defeasible logic decision plugin.