Once, writers dwelt quite apart from their readers. One hand clasped to a palely domed forehead, they wrestled to order their words and ideas in rooms where the joy of solitude was poignantly coloured by a whisper of loneliness. Here blundered no uncomprehending reader. Their contact with the writer, if any, came through the word on the page, enhanced, perhaps, by a mildly salacious biography that shed a little light on the character and intent of the work's creator. Marketing, and in its wake festivals, changed all that. If, in the respectful exchanges that take place in draughty marquees, tales of verbal assault are few, still this is a new relationship. Today's writer has to reach out not through the power of their work so much as by the appeal of their personality. But with the uninhibited intimacy of Twitter perhaps a watershed has been reached. As Joe Simpson, the death-defying mountaineer, who has with Touching the Void summitted the marketing man's Everest by writing what has become a GCSE set text, now knows, some tweeters see no limit to the invective that can be squeezed into 140 characters. Just messed up GCSE English? Tell your tormentor who's at fault. "I failed because of you," read one tweet from Turkey to Simpson. From England, "Three chapters of crawling … was rather boring." They should not have expected the man who got himself down a mountain with a broken leg to flinch. His last word: "good night vile innocents may you all seethe in bilious acid pus."