I was interested in re-purposing this example on using PostGIS from within R. It assumes that “an ODBC connector has been set up”. It did take me a while to set up the connection from R on a Mac (OS 10.5.8), and I did not find a coherent documentation about this.
So for the record, below is how I did it.
The process included installing the Postgres driver, setting the configuration file for the ODBC connection, and then using odbcDriverConnect from within R to open the connection.Mas:

http://www.stanford.edu/~cengel/cgi-bin/anthrospace/how-to-access-a-postgres-database-from-r-on-mac