Adding local 'DNS' entries to your mac

I'm currently working on adding subdomains to my sinatra app - following the instructions at:
http://tannerburson.com/2009/01/extracting-subdomains-in-sinatra.html

First we need to add a local domain name to our hosts file:
http://decoding.wordpress.com/2009/04/06/how-to-edit-the-hosts-file-in-mac-os-x-leopard/

• sudo vi /private/etc/hosts
• Run dscacheutil flushcache

Once this is done, wildcard subdomains will need to be supported. I'm using Heroku, and thus I'll follow the instructions at http://devcenter.heroku.com/articles/custom-domains