简言之， 忘记heroku, 尽情的使用linode吧， 260块钱一个月，2G内存， 用起来跟独立的机器一样。 而HEROKU把太多LINUX 的功能抽取出了service, 用起来不方便，而且一旦脱离了heroku 环境，你发现自己将失去一切。
linode 使你成为 前途光明的 LINUX 专家。
I prefer linode, aws or so.
linode : is a standard linux server. you can login, install 3rd party dependencies and play around just like in your own server. Installing nginx/rails/ruby is the same way as what you did on your own pc/laptop/server.
heroku : is a service. I have learn lots of stuffs that is not valuable if one day you switch to another platform(e.g. linode) or you have your own real server. for example, check the logs, install databases, or install gems. I have printed out most of its documents and read them in 1/2 days, and then I realize that I can't use this knowledges in my working server( that my company offered to me)
linode is cheap enough, $20 per month.
heroku is not always free. and I don't think it's stable enough for demonstration purpose.(e.g. your free heroku app will fall in sleep in spare time, and will cost your several seconds to wake up. this SEVERAL seconds is long enough to make you lost your customers if they want FAST web app )
so, forget heroku, buy or setup your own VPS, use it for years, then you will be an linux expert.