Drush 5 has an amazing new feature called "Quick Drupal" that downloads Drupal, sets it up, runs it in an embedded webserver and launches your web browser to the site, already logged in as admin. All in less than 30 seconds. It's ridiculously awesome.
Unfortunately, Drush's embedded webserver won't run on Mac OS X out of the box. PHP-CGI is required, and that does not come preinstalled in Max OS X. (I'm running Lion, so perhaps other versions have it, but Lion does not.) After half and hour of Googling, I came across what ended up being a pretty easy solution. I'm posting it here to hopefully save future Googlers some time.