For future reference, it might be a good idea to not upgrade blindly on a day when you expect a lot of hits. You might try setting up a test site where you can try these things first. Just a friendly suggestion if you are not already doing it.
Turns out I accidentally uploaded a home.php file with my template when I built my new site. I am not sure why WordPress looks at home.php before index.php since that makes no sense by common web practices, but that was my problem. I would check to make sure your template directory does not have a file along these lines. I found it by simply comparing which files were in the default theme directory versus my theme’s directory.
I had just built a test site using version 2.7.1. When I went to build my real site, I went to version 2.8. I instantly ran into this exact same problem. How does something like this not get picked up in QA?!? At least I know to be very cautious when upgrading now.
