Blotter is a new service from Dapper that graphs a blog's popularity over time. The popularity statistics are gathered from Technorati using the Dapper service.
Stats are based on Technorati Ranking over time (start date 05/08/07):
See the Blotter site for how to embed your own graph - its just a case of cutting and pasting one line of html.
See also Technorati's guide to how it rates a blogs authority.