This is good idea. I will work on it. Now, if you can add common description for all categories, over categories list (yourqa.com/categories) add:
in file qa-page-categories.php after line 85 where is $qa_content['title']=qa_lang_html('misc/browse_categories');
$qa_content['custom'] = 'your general description';
You can use html code here, and php of course too. This is hack no plugin, so use it if you need it only. I will work on plugin, but maybe somebody working on it already.
can anbody run syntax higlander here for code? :)