This reminds me of when Posterous.com ended it’s blogging service. At the time I had like 5-6 blogs with them. I’ve never recovered those blog posts.
That’s what I’m concerned about with Medium. Sure it seems like the place to be have a 3rd party blog host, but they could shutter at any moment, leaving you stranded.
Any important services, especially data or content hosts, host these yourselves, and don’t rely on 3rd party / cloud hosting. You could and will be burned.
Maybe I’m just not an early adopter.