Until tonight, we'd no idea that David Letterman was so painfully ignorant about Twitter. He thinks it's something people have to pay for! So Kevin Spacey pulled out his Blackberry and attempted to explain it all to him.
This obviously didn't go very well as Spacey, who posted a tweet to his Twitter page during the demonstration, got this response from Letterman after he'd concluded his tutorial: "You know what it reminds me of? Oh yeah, a waste of time!"