I'd like to know what is a correct way to set up permissions for directory /var/www/example.com and all the files in it. The entire server will be used to set up my sites only so I'm not sure if it is even necessary to create a new user for each of my site. Apache runs as www-user:www-user. It would be also great if you could explain a little from security point of view.
EDIT It looks like I do need to run 2 sites as separate users simply because one of the sites will have to be as secure and as separated as possible from the other, which I expect to be much more vulnerable (vbulletin forum). Being able to compromise supposedly secure site through less secure one is unacceptable for me.