In this new post to his blog Davey Shafik looks at a problem plaguing several mailing lists out there (including some of the PHP ones) - that they're a "free for all". What's his solution to help it? Karma.
In the real world, communications pass through a hierarchy of people, escalating as necessary, passing from person to person up the chain. This means that, given enough time, any mailing list starts to have a large noise:signal ratio, at least for any given person's take on the list; they want to read what they want to read, and don't need to be distracted ignoring the stuff they don't want to read.
His solution involves defining a hierarchy for the lists and the karma attached to them (based on user CVS level or a timescale or other measurement) to allow the "more interesting" things to filter back up to the correct places. His examples use some of the PHP lists as a sample structure.