+Specify node and npm version: https://devcenter.heroku.com/articles/nodejs-versions/.
+Also, if you need to execute an NPM in a `postinstall` hook in package.json, you'll get `sh: npm not found` on Heroku. So, add `"npm": ">= 1.1.1"` to your package.json.
+Another random note. Tower has coffee-script and coffeecup modules installed in a `postinstall` script defined in package.json. If you add coffee-script to your app's package.json (pointing to the same custom coffee-script fork), it will install it twice and there's a weired error having something to do with `chmod` and permissions on `..../bin/coffee`, _on heroku only_, probably because it's trying to remove the `coffee` command from within coffeecup - since it's installing `coffee-script` again. Just add the regular `coffee-script` dependency in your package.json if you get this error.