Postach.io takes the post you put in a notebook on Evernote and serves it in a blog hosted on Amazon Web Services. This technical stuff happens in the background so, from the user's point of view, the result is a really simple way to blog, with the added security that every blog post is synchronized both on Evernote and on one's home computer.
In addition, Evernote has just improved its security in order to allow third party authorization only for a single notebook, which means that using Postach.io with Evernote is also much more secure than in the past.
I used Postach.io for a short time, but stopped mainly due to Evernote's poor integration with Linux. Unlike, say, Dropbox, the only way to use Evernote offline on a Linux desktop is to rely on third party solutions that are much poorer than the native Evernote desktop interface. So, in order to use Postach.io, it was necessary to write online - in which case I may as well use WordPress, or use one of these Evernote 3rd party options. In addition, post-Snowden, I started to think about privacy issues and stopped using Evernote for other kinds of notes. Nowadays I simply use Emacs Org Mode for my notes.
Postach.io has also introduced blogging via email - just as many blogging platforms including WordPress do - but that doesn't work for me as I always need to edit and re-edit whatever I write.
For someone who is not a Linux user and loves Evernote, Postach.io is a clever solution.