This is something I'd personally use. A lot of alternatives exist on the market but none of them look as refined as Paper.
Paper looks really similar to http://onword.co (by Daniel Eden at Dropbox) regarding the minimalism and limitation on formatting. I guess Hackpad team is working on the backend.
I just hope this project will not end up like Mailbox. I've been using Mailbox on OS X for half a year. Although once in a while I encounter some bugs, it's still very usable. A few months ago, they released an upgrade from 0.4 to 0.7. The UI became uglier in orders of magnitude and many basic functionalities just broke. After experiencing it for 3 days I switched back to Mail.app. I have sent quite a few bug reports and suggestions, but got no response. I wonder if they still care about Mailbox at all.