When I worked in theater, I was always writing things on Post-it Notes and sticking them on screens or desks. Twitter has given me a way of continuing to post those notes, only a lot of other people see them, too.
I've heard people on panels say, 'You must have a Web site. You need to tweet. Repeat the title of your book constantly,' and I just want to say, 'Shut up. Everything you're saying is wrong.' People will know instantly if your only motivation for tweeting is to sell books.
'Harry Potter' achieved a very special act of actual magic: it made it completely acceptable for an adult to carry around, read and enjoy a children's book.
I read two mysteries a day when I was a kid. All of Agatha Christie, all of 'Sherlock Holmes.' I've seen every single British detective show ever made.