Google Trends is now competing directly with services such as Alexa and Compete, by allowing users to look at trends by website address.
Whereas previously Google Trends only offered data on search terms, you can now see website traffic data over time as well as comparing traffic between different sites.
For users with a Google account, Trends will display a numerical scale on the graph, to give you more of an idea about traffic volumes.
Both Alexa and Compete get much of their traffic data from users who have installed their toolbars, so this can produce a limited picture of website visitors.
However, Trends takes its figures from search data, opt-in anonymous Google Analytics data, as well as some third party research. This potentially means that Trends will give a more accurate picture than its rivals. .
Google Trends provides a chart showing daily unique visitors, while users can compare two or more websites side by side:
Trends also provides further data on the geographical spread of a website's visitors, as well as a list of other sites visited by the same users and other keywords they have searched for:
This is a useful feature from an SEO perspective as it's a good way to find some useful keywords, as well as seeing what other sites your audience is visiting.
SEO Roundtable Briefing - May 2008