The Places frecency algorithm - MDC
https://developer.mozilla.org/en/The_Places_frecency_algorithm
"Frecency is a score given to each unique URI in Places, encompassing bookmarks, history and tags. This score is determined by the amount of revisitation, the type of those visits, how recent they were, and whether the URI was bookmarked or tagged. "
The Danger of Aggregate Displays in Social Software - Bokardo
http://bokardo.com/archives/the-danger-of-aggregate-displays-in-social-software
"Where is the ethical line drawn when designing interfaces that show popularity?"