Starting Apache2 on Mountain Lion
sudo apachectl start starts Apache and enables /System/Library/LaunchDaemons/org.apache.httpd.plist.

To make http://localhost/~username/ work, save something like this as /etc/apache2/users/username.conf:

&lt;Directory "/Users/username/Sites/"&gt;
    Options Indexes MultiViews
    AllowOverride All
    Order allow,deny
    Allow from all
&lt;/Directory&gt;


I didn't have to edit any other files or httpd.conf.