Book critic David Kipen expected to hear from a few disgruntled readers when he gave the latest Harry Potter book a lukewarm review. What he didn’t expect was the death threat. “When somebody e-mails to say, ‘Seriously bitch u need to watch what teh f — you say,’ it certainly commandeers a critic’s attention. Add to that the dozens of correspondents who took the trouble to call me dork, idiot, schmuck or worse, and it’s all occasioned some serious soul-searching here on the literature desk.”