As much I like mattt's work, I dont understand, why is this needed. brew install postgres is just as easy and in my experience Postgres.app is not well maintained and uses an older version.
I suppose osx built-in installation may cause conflicts.
This is a consistent source of trouble when installing Postgres. Usually, this involves looking up the right places to modify the path and sometimes needing to change permissions/ports.
http://stackoverflow.com/questions/12472988/postgres-could-n...
postgres app fixed it
While it is really easy to install most of the time, I'd say the Postgres.app works well for people who aren't developers but need to use PostgreSQL.
initdb /usr/local/var/postgres -E utf8
Also if you are working with rails, add host: localhost in your database.yml file and remove the user password. That should be all you need.
This is probably "elitist" of me but I feel like someone who isn't comfortable with the command line should be learning that before they tackle Postgres.