I built and deployed
http://rubytu.be/ on Heroku. Since it was just a
little site to scratch an itch and I'm not consuming much DB space or
resources, Heroku was perfect for a free host. It couldn't have been
easier to work with and deploy to. And if ever necessary, I can
simply bump up the number of app instances on the fly with little to
no work.
Haven't had any issues and a push to production is a quick "git push
heroku" away (which is pretty awesome).
Grab a free account and play around with it. You could register and
deploy a test app in literally a minute or two.
-MW