Awhile ago if you had asked me about free, super-easy Rails hosting, I would have blown your mind by mentioning Heroku -- cloud-based Rails hosting. FREE cloud-based Rails hosting.
Lately, though, I'm not so sure.
Check out the Heroku Google Group. There are a lot of complaints there, and no one from Heroku is talking. Seeing "my website has been down for 4 days," and then seeing another say "mine too" without any response from the Heroku team is enough to put you on edge. But, maybe these issues are getting handled, and they back-and-forth just isn't taking place on the group. If so, maybe Heroku should think about having their own ticket system or something in place, because as it stands now, all the unaswered complaints are casting a bad light on the service as a whole.
All that considered, if you're looking for an extremely easy way to deploy a trivial little app, Heroku might be for you. I've got my own VPS, but lord knows using Heroku would be a lot easier... but I'll wait until they come out of beta for that.