Audience Building: Social Media Common Sense

Facebook and Twitter may still be trying to figure out how to make money, but what will inevitably be their "common sense" solution, should also all be all filmmakers "best practices".  By no means am I encouraging spam, but what the studios pay firms big money to do, anyone with some time on their hands can make a noble effort of themselves.

Isn't listing your favorite film or book an invitation to be contacted when someone has something similar to offer?  Say your film is playing at the Ashland Oregon film festival; wouldn't you search the network in that region and then search for folks who liked a similar film as yours?  If you were a fan and you got a personal invite from the filmmaker to come check out the film at the festival, wouldn't you be tempted to go?  Shouldn't this be standard practices for all filmmakers?
Who is doing this now?  How successful is it?  What tips do you have for the rest of us?