I turned on the Multisite options, backing up the wp-config.php and .htaccess file as directed. After playing for a while, I turned it back off (copied the wp-config and htaccess files back).
Now, there are plugins that "know" my site is set up for multiple blogs and get confused. How can I revert to a single blog with no extraneous bits and pieces? I'm assuming it will involve editing or dropping SQL tables, but I don't want to destroy what I have just to enable one or two inessential plugins (Google Sitemap being primary).