13. A system for selecting key phrases for providing context-relevant content to users, comprising: a computer system comprising one or more computers, said computer system programmed with executable code modules to at least: identify a key phrase that appears on a page of a publisher site; generate a score for the key phrase based at least in part on view counts of social media content items associated with the key phrase, said social media content items being accessible to users on one or more social media sites that are separate from the publisher site, wherein the computer system is programmed to generate the score by a process that comprises determining, based at least partly on the view counts, whether a rate of consumption of social media content associated with the key phrase is increasing; and determine, based at least partly on said score, whether to use, or to suggest use of, the key phrase for selecting contextually-relevant content to present on the publisher site.
13. A system for selecting key phrases for providing context-relevant content to users, comprising: a computer system comprising one or more computers, said computer system programmed with executable code modules to at least: identify a key phrase that appears on a page of a publisher site; generate a score for the key phrase based at least in part on view counts of social media content items associated with the key phrase, said social media content items being accessible to users on one or more social media sites that are separate from the publisher site, wherein the computer system is programmed to generate the score by a process that comprises determining, based at least partly on the view counts, whether a rate of consumption of social media content associated with the key phrase is increasing; and determine, based at least partly on said score, whether to use, or to suggest use of, the key phrase for selecting contextually-relevant content to present on the publisher site. 19. The system of claim 13 , wherein the computer system is programmed to use the score to determine whether to suggest use of the key phrase for selecting contextually-relevant content to present on the publisher site.