This is ad was running on Salon today and linked to the Salon Media Twitter. Salon's had the twitter account since late October. In the ad Salon asks "Do You Tweet?" They also say "We do. All day long."
Raw Story is another example of a news outlet pushing its Twitter. They currently have a a button on rawstory.com promoting their Twitter account which is @rawstory.
It's an indication of how important Twitter has become to news organizations. More and more people are receiving news updates on Twitter so major media outlets -- and even some blogs that might be a little late to the party - are now actively promoting their twitters to try and increase subscribers.
You can find more twittering news services here on the Twitter Fan Wiki.
This is ad was running on 
