Question: I have multiple well-established Wordpress sites.

I am considering combining them into one Wordpress MU site. I have found that a few of the sites probably do not get as much of my attention as they should. I think this may simply be because they are "out of sight, out of mind." I believe with all sites in one dashboard, they will get much more attention.

Is this the way to go? What is the best method to combine the sites? I haven't been able to find a tutorial or really too much information.

Answer: 
Do you have any custom post types? Is there any chance that a page or post is using the same slug as a custom post type?

Also, does your home page work or is it a 404 for all pages?
As I was always getting a server generated error, a friend of mine pointed out that this meant the `.htaccess` file was not even being read.

He advised checking the `.conf` file for the site, and sure enough, there was a typo in the `<Directory /var/www/...>` entry, meaning that the directory was not being read correctly when a user visited the site.