I\'ve installed a few basic apps on Heroku without problem, and this one (Rails 3.1.3) seemed fine in that it showed Rails welcome page
public/index.html.
It looks like you may not have precompiled your assets before you pushed to Heroku, try:
rake assets:precompile git add . etc etc
I think that should help. For more information, see here: http://devcenter.heroku.com/articles/rails31_heroku_cedar