I did a crawl of the Alexa Top 1 Million, a list of the top 1 million most visited sites on the web. During the crawl I was tracking the use of security based HTTP response headers but I also checked for certificates issued by Let’s Encrypt. Here are the results:
Out of the 1 million most visited sites on the web (Feb 2016), Let’s Encrypt already issues certificates for 1,234 of them! You can read more details and look at the other metrics I recorded, as well as downloading the raw data, on my blog.