It would be great if we could get a list of user ids that are configured to receive notifications, a la 
the block/ids call. This would allow us to more easily process messages from users for whom the 
logged-in user has assigned some additional importance.

Yes, could could probably use the friendship/show method to get this same data, but it would 
require significantly more requests to twitter and wouldn't scale as well for us, since we could 
theoretically be talking about 1 friendship/show call per message.