[emin-gun-sirer]

Let me use this opportunity to point out http://virtual-notary.org, an online witness to facts that can be checked online, where these facts are recorded in the Bitcoin blockchain. These go beyond the types of document proof of existence cited in the article, and can cover facts such as exchange rates, DNS address ownership, WHOIS info, weather conditions, housing prices, employment status, etc.

This article describes the usage scenarios in detail: http://hackingdistributed.com/2013/06/20/virtual-notary-intr...