To start using Dotenv now it is very simple.

One include the library

#composer.js
	"require": {
          "laravel/framework": "4.2.*",
          "vlucas/phpdotenv": "1.0.*@dev"
    },

Two update your start.php

#bootstrap/start.php line 27
Dotenv::load(__DIR__ .'/../');


$env = $app->detectEnvironment(
    function()
    {
        return getenv('APP_ENV');
    }
);

Make sure to set your .env file

#.env
APP_ENV='local'

That is it you are set to use it for all your environments.

Update

For Heroku I used this instead

$env = $app->detectEnvironment(
    function()
    {
        if(!isset(getenv('APP_ENV')))
        {
            Dotenv::load(__DIR__ .'/../');
        }
        return getenv('APP_ENV');
    }
);

Setting the initial APP_ENV using heroku config:set APP_ENV=stage