Google has this new search option where you can search the latest twitter feeds (and maybe other things, I'm not clear on that). You can either look at them in the browser or be sent alerts by email (I haven't tried that, so I don't know if it's gmail only).
You can search for any terms. For example, if you search for "silent movie" today, you will find that Hugh Hefner sent out a twitter that they are showing Doug Fairbanks' Robin Hood tonight, August 28, 2010, at the mansion.
But you can also go back in time to find out who was saying what, when. Wait until the lawyers get a hold of this.
Site FAQs, calendar of festivals and other helpful tools.