Using instructions from http://www.pjgalbraith.com/2011/08/recent-posts-plus/ (Item 11 on the graphic) I have attempted to show posts from only one of my three categories.
In WP_query Options field for the widget I have this:
"cat": "5, -6, -1",
I want to display cat 5 but not 6 or 1.
Still, cat 6 is showing up.
Cat 1 has no posts anyway.
The site in question is http://www.world-widemovers.com.
The widget is on the top left sidebar.
You will see a Vacation Planning post which is in cat ID 6.