- sudo su postgres
- supply your Mac password
- modify /Library/PostgreSQL/9.x/data/pg_hba.conf
- from local all all md5
- to local all all trust
- execute /Library/PostgreSQL/9.x/bin/pg_ctl restart -D /Library/PostgreSQL/9.x/data/
- run psql
- change postgres password
- ALTER USER postgres WITH ENCRYPTED PASSWORD 'password';
- modify pg_hba.conf back
- restart again
Tested with PostgreSQL version 9.1 OSX Lion