This is a huge feature. It means that with Heroku and a static site you can build your own (free!) Dropbox powered blog. You don’t need to deal with git deployment at all; you just put your files into a Dropbox directory, hit the “Deploy” button in your Heroku dashboard and there is no third step.
I haven’t tried the new feature yet (which Heroku calls “Beta”), but if it works as advertised this is huge for making blogging on Heroku more accessible.
The only problem is that with Jekyll1 you’ll still have to build your site locally first – but Heroku has the theoretical ability to build stuff from source server-side. It looks like this might be possible with Jekyll, but I haven’t looked into that too deeply.