In configuring Apache 2.2.19, I changed the default (when installed from source) directory from apache2/htdocs to /home/www. I created a user & group www, a /home/www directory, copied my default "It works!" index.html file to there, changed owner:group permissions to www:www, and modified my .conf files to point to /home/www.

Then Apache stopped serving files...??

Looking at the original apache2/htdocs, ../cgi-bin, ../error, and the files therein, they're all set to 500:500. Who the heck is 500? There's no mention of such a user or group 500 in /etc/passwd or /etc/group. However, when I changed permissions of /home/www & files to 500:500, Apache works.

I have no idea how or where Apache is receiving the directive for 500:500, though I looked through all the .conf files , and any search for Apache & 500 pulls up results for Error 500. How and what do I change so that Apache accepts www:www as owner:group?

You don't indicate which distribution of Linux you are using. They are not all the same in their configuration.
Most of the time, there is a public_html directory in the /home/user directory and the apache configuration has an entry for user directory and it usually points to public_html directory. Is there some reason you did it the way you did?

The uid 500 is usually the first normal (no-root) user created. I don't know how to find the user from the uuid but if you enter your user name and don't have too many users you could find it. Open a terminal and type: id user (change user to whatever the real user is/are).

<-- *points to the "Distribution: Debian 5 + Xfce" in his posts' info box*
Quick way: getent passwd [uid]. Slow way: vi /etc/passwd.
Helps if you restart Apache. Duh. It works now. Don't mind me. LOL! I'd be curious to know who or what username 500 is, though, as they don't seem to exist. *shrug*