I installed Postgresql on my Mac in order to use Heroku.

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ brew install postgresql
Warning: Your Xcode (4.4) is outdated
Please install Xcode 4.4.1.
==> Downloading http://ftp.postgresql.org/pub/source/v9.1.4/postgresql-9.1.4.tar.bz2
Already downloaded: /Library/Caches/Homebrew/postgresql-9.1.4.tar.bz2
==> Patching
patching file src/pl/plpython/Makefile
patching file contrib/uuid-ossp/uuid-ossp.c
==> ./configure --disable-debug --prefix=/usr/local/Cellar/postgresql/9.1.4 --datadir=/usr/local/Cel
==> make install-world
==> Caveats
# Build Notes

If builds of PostgreSQL 9 are failing and you have version 8.x installed,
you may need to remove the previous version first. See:
  https://github.com/mxcl/homebrew/issues/issue/2510

To build plpython against a specific Python, set PYTHON prior to brewing:
  PYTHON=/usr/local/bin/python  brew install postgresql
See:
  http://www.postgresql.org/docs/9.1/static/install-procedure.html

# Create/Upgrade a Database

If this is your first install, create a database with:
  initdb /usr/local/var/postgres

To migrate existing data from a previous major version (pre-9.1) of PostgreSQL, see:
  http://www.postgresql.org/docs/9.1/static/upgrading.html

# Start/Stop PostgreSQL

If this is your first install, automatically load on login with:
  mkdir -p ~/Library/LaunchAgents
  cp /usr/local/Cellar/postgresql/9.1.4/homebrew.mxcl.postgresql.plist ~/Library/LaunchAgents/
  launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

If this is an upgrade and you already have the homebrew.mxcl.postgresql.plist loaded:
  launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
  cp /usr/local/Cellar/postgresql/9.1.4/homebrew.mxcl.postgresql.plist ~/Library/LaunchAgents/
  launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

Or start manually with:
  pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start

And stop with:
  pg_ctl -D /usr/local/var/postgres stop -s -m fast

# Loading Extensions

By default, Homebrew builds all available Contrib extensions.  To see a list of all
available extensions, from the psql command line, run:
  SELECT * FROM pg_available_extensions;

To load any of the extension names, navigate to the desired database and run:
  CREATE EXTENSION [extension name];

For instance, to load the tablefunc extension in the current database, run:
  CREATE EXTENSION tablefunc;

For more information on the CREATE EXTENSION command, see:
  http://www.postgresql.org/docs/9.1/static/sql-createextension.html
For more information on extensions, see:
  http://www.postgresql.org/docs/9.1/static/contrib.html

# Other

Some machines may require provisioning of shared memory:
  http://www.postgresql.org/docs/current/static/kernel-resources.html#SYSVIPC

To install postgresql (and ossp-uuid) in 32-bit mode:
   brew install postgresql --32-bit

If you want to install the postgres gem, including ARCHFLAGS is recommended:
    env ARCHFLAGS="-arch x86_64" gem install pg

To install gems without sudo, see the Homebrew wiki.
==> Summary
/usr/local/Cellar/postgresql/9.1.4: 2751 files, 36M, built in 117 seconds

Initializing Database

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ initdb /usr/local/var/postgres
The files belonging to this database system will be owned by user "yamadanaoyuki".
This user must also own the server process.

The database cluster will be initialized with locale ja_JP.UTF-8.
The default database encoding has accordingly been set to UTF8.
initdb: could not find suitable text search configuration for locale ja_JP.UTF-8
The default text search configuration will be set to "simple".

creating directory /usr/local/var/postgres ... ok
creating subdirectories ... ok
selecting default max_connections ... 20
selecting default shared_buffers ... 1600kB
creating configuration files ... ok
creating template1 database in /usr/local/var/postgres/base/1 ... ok
initializing pg_authid ... ok
initializing dependencies ... ok
creating system views ... ok
loading system objects' descriptions ... ok
creating collations ... ok
creating conversions ... ok
creating dictionaries ... ok
setting privileges on built-in objects ... ok
creating information schema ... ok
loading PL/pgSQL server-side language ... ok
vacuuming database template1 ... ok
copying template1 to template0 ... ok
copying template1 to postgres ... ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the -A option the
next time you run initdb.

Success. You can now start the database server using:

    postgres -D /usr/local/var/postgres
or
    pg_ctl -D /usr/local/var/postgres -l logfile start

Starting Server (Manually)

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start
server starting

Displaying list of database

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ psql -l
                                         List of databases
   Name    |     Owner     | Encoding |   Collate   |    Ctype    |        Access privileges        
-----------+---------------+----------+-------------+-------------+---------------------------------
 postgres  | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 template0 | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/yamadanaoyuki               +
           |               |          |             |             | yamadanaoyuki=CTc/yamadanaoyuki
 template1 | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/yamadanaoyuki               +
           |               |          |             |             | yamadanaoyuki=CTc/yamadanaoyuki
(3 rows)

Console Login

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ psql postgres
psql (9.1.4)
Type "help" for help.

postgres=#

Logout from console

postgres=# \q

Create User, create DB

Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ createuser -P postgres
Enter password for new role: 
Enter it again: 
Shall the new role be a superuser? (y/n) y
Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ createdb mydb -U postgres
Yamada-Naoyuki-MacBook-Pro:~ yamadanaoyuki$ psql -l
                                         List of databases
   Name    |     Owner     | Encoding |   Collate   |    Ctype    |        Access privileges        
-----------+---------------+----------+-------------+-------------+---------------------------------
 mydb      | postgres      | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 postgres  | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 template0 | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/yamadanaoyuki               +
           |               |          |             |             | yamadanaoyuki=CTc/yamadanaoyuki
 template1 | yamadanaoyuki | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/yamadanaoyuki               +
           |               |          |             |             | yamadanaoyuki=CTc/yamadanaoyuki
(4 rows)