I installed supercache this morning, then started to get a few emails from friends saying they couldn't access the site. Sure enough, when I refreshed the page myself I got the following 403 Forbidden error:
You don't have permission to access / on this server.
You may need to create an index.html page or enable the directory browsing by creating an .htaccess file containing "Options +Indexes".
I've uninstalled supercache according to the instructions, (removed directories, changed .htaccess back, wp-config.php, etc), but...I'm still getting the error.