12. A system for selecting key phrases for providing contextually 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 site; and 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 said site, said score representing a suitability of the key phrase for selecting contextually relevant content to present on the page, wherein the computer system is configured to generate the score by a process that comprises assessing, based at least partly on the view counts, a rate of change in a popularity level of the key phrase.
12. A system for selecting key phrases for providing contextually 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 site; and 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 said site, said score representing a suitability of the key phrase for selecting contextually relevant content to present on the page, wherein the computer system is configured to generate the score by a process that comprises assessing, based at least partly on the view counts, a rate of change in a popularity level of the key phrase. 14. The system of claim 12 , wherein the computer system is further configured to use the score to determine whether to use the key phrase for selecting contextually relevant content to present on the page.