Hmmm, when you are sitting there watching the major news outlets and they are asking you to follow them on Twitter, it has become a household name to me. ;)
Rachel Maddow (@Maddow) uses Twitter quite effectively. She even had a segment on the Twitter Terrorism thing the other night.
I thought so too until some meathead convinced me to join on 2008-07-24. I haven't looked back since. Twitter was instrumental in helping me obtain a Newsweek home page reference and a Financial Times reference. We sold out of product yesterday. Site only live for 30 days. Ranks #1 out of 6,000,000+ for its targeted generic phrase too.