I've asked a number of professors this question and received largely the same answer from all of them: it probably can't hurt you, but it probably can't help you either. Some professors find it to be a bit transparent and thus off-putting. Others say that while they always respond politely, there is rarely anything of substance to say before reading someone's application. All of them agree that contacting professors is unlikely either to sink a good application or to tip the balance on a so-so one. As to the admissions anecdote about the applicant who was only rejected from those schools at which she didn't contact professors, I offer this: maybe the student only reached out to professors who were a good "fit" and/or did more research in order to bulk up the content of the email. Either way, the emails themselves didn't make a difference: you are always more likely to get into schools at which you are a good fit and about which you've done research.