One of the sites I host was not working this morning, but I tracked down the problem and fixed it, so I thought I would share what I learned. If you have the following line in your .htaccess file, it is apparently not supported by Apache 2.2, and it must be removed for your site to load:
This is a common .htaccess tweak that is required to fix FrontPage publishing issues, and is recommended in other TCH forum threads. I'm not sure what impact removing it will have on the ability to publish but at least the site is up again. I'm also not sure if this setting is used for anything else.
Before upgrading any more sites to Apache 2.2, this probably needs to be investigated and users with this setting will need to be warned.