Twitter. Best one I've read yet. Money quote:
Kafka would have had a Twitter feed! And so would have Hemingway, and so would have Virgil, and so would have Sappho. It's a tool for writing. Heraclitus would have had a f***ing Twitter feed.
Tip o' the mug to Alexis Madrigal, who tweeted a link that took me to this, but I ended up there instead. (If that makes sense.) (Makes sense in the e-world, right?) (Which is another way of saying that Twitter is also good to read.)