Last year, when I asked couch.io for an account, they suggested that I go with a competitor cloundant because they were not ready for users. It really impresses me when companies/people show such honesty. I expect that now both couch.io and cloudant will do a good business (as will MongoHQ): as easy as it is to run services on our own servers, it is also great to just let someone else worry about admin (like using Heroku, for example)

{"error":"bad_request","reason":"invalid UTF-8 JSON"} when i try signing up

looks like, no. sign up on the front page for an instance.

http://www.couch.io/get

Nope, just sign up :)