Just a quick note – perhaps this might help somebody googling around for the problem I was having.

If you upgraded from Tiger to Leopard and you are playing around with Apache you will notice that if you try to access http://localhost/~username it will give you a forbidden message.

Problem: There is no username.conf in /private/etc/apache2/users/

Reason: I assume this is because it is genereated only when you create a new user. Since Apple upgraded to Apache 2 with Leopard the paths are slightly different.

Solution: Simply run the following command to copy your old username.conf to the current directory:

sudo cp /private/etc/httpd/users/[your username here].conf /private/etc/apache2/users/

After copying the file restart apache.

Result: Hopefully a working apache install.