I am also having trouble getting this to work. I have set up the plugin to disable the guest sidebar and utilize one of my theme sidebars. I then choose that sidebar for the particular page where I'd like the user-based sidebar. I populate that sidebar with widgets and when I go to the page logged in to that user role, I see the theme sidebar content I set to be replaced.
Any ideas on what I am doing wrong here? Like Bainternet, I am using a User Role plugin in addition to the Sidebar per User Role. Could there be a conflict between those two plugins?