SF often talks about reputation systems as part of a society's culture. True, it's a big hairy problem, but how could some person or group make an initial attempt at doing this? It'd be great to have web pages, tweets, and various posts tied somehow to a measure of the author's current trustworthiness (based on previous behavior). Even a high/medium/low/unknown rating would help.
No matter how imperfect the implementation might be, it'd be great to have anything that exposes to the general public the idea that people need to consider the source of anything that's posted on the Internet.
What would you try doing?