I’m also using WP 3.3.1 and the latest version of the better background plugin. I also configured NextGEN Gallery as it recommended and configured all the settings correctly, but no background image is shown.
Scroll down to the bottom of the page where it says “Related Posts” and you’ll see some posts have a thumbnail there but others don’t. Is there a way to have the posts without any images automatically revert to a default image?
For people who have this problem in the future, go to the dashboard, then settings > permalinks. Set the permalinks setting to default then back to the setting you want. And make sure your .htaccess is writable.