How to find pg_config path

sudo find / -name "pg_config" -print

The answer is /Library/PostgreSQL/9.1/bin/pg_config in my configuration (MAC Maverick)

Installing homebrew

/usr/bin/ruby -e "$(curl -fsSL https://raw.github.com/gist/323731)"

And then installing postgresql

brew install postgresql

gave me this lovely bit of output:

checking for pg_config... yes

ahhh yeahhhhh

I recommend that you try to use Postgres.app. (http://postgresapp.com) This way you can easily turn Postgres on and off on your Mac. Once you do, add the path to Postgres to your .profile file by appending the following:

PATH="/Applications/Postgres.app/Contents/Versions/latest/bin:$PATH"

Only after you added Postgres to your path you can try to install psycopg2 either within a virtual environment (using pip) or into your global site packages.