URL Trends was developed by Joel Strellner to allow Webmasters, Search Engine Optimizers, and domain buyers to determine a websites (or a specific pages) rankings in the various search engines and directories. Based on this information you can make competitive analysis of any website with another website — and from this you could possibly determine whether your SEO tactics are positive or negative to your website; or, if you are a domain buyer, determine if a particular domain should be purchased.
Url Trends was designed from the beginning to have a different approach to viewing link popularity and other pertinent information. The theory was that webmasters would like to be able to see their link popularity stretched out over time, not just for the current day. This unique approach to viewing the information allows people to make a truly accurate judgement of the website and not be subject to artificial inflation that the instant link popularity reports suffer from.
Currently, URL Trend Report allows webmasters to view their linking trends for eight different search engines (Google, Alexa, Yahoo!, MSN, AllTheWeb, Alta Vista, Teoma and Gigablast), as well as the PageRank and Alexa Rank. A recent addition also allows them to view the number of end-users of the website that bookmarked their website using Furl or Del.icio.us.
Source: About URL Trends