From the newsletter:

When I saw the Kindle clipping pop up this morning, I felt a rush of "aw, I loved that book!" and of course my first impulse was to tweet it, which is a statement approximately equivalent to: my first impulse was to write it on a slip of paper and throw it into the wind. It doesn't work anymore, Twitter; not for things like this. Appreciations, recommendations -- they are swept away and the people who ought to see them, don't.