The PostGIS experience on mac is a very slick and slippery slope.
First of all the Installers are very Slick
There are a series of nice mac installers that have been bundled up by William Kyngesburye.
And the installers are very good about beeping at you and asking you to install GDAL and PROJ prior to postgis.
And then the slippery ...
The installer don't provide much guidance on where things went ... I am used to having a postgis_template created for me by the windows installers. And all my notes are based on creating new database using that as a safe starting place.
Here were the steps needed to create my own postgis_template:
1) cd /usr/local/pgsql/bin (and then use ./ to get it to pick up the commands)
2) ./createlang plpgsql template_postgis -U postgres
3) ./psql -U postgres -f /usr/local/pgsql/share/lwpostgis.sql template_postgis
4) ./psql -U postgres -f /usr/local/pgsql/share/spatial_ref_sys.sql template_postgis
Other then that pgAdmin looks quite happy.