One thing I noticed about that category plugin is that it only displays a single post's content. It won't display the contents of all posts under a category when the category is selected. I don't know if it was like that with this plugin for previous versions of WP, but it is for 2.3.
Also, it only displays five post titles for each category, not all the titles under that category. Ideally, it should show all the post titles in that category, and ONLY that category (in addition to the aforementioned post contents of all posts under that category, as the default does). What I mean is that if there are child categories under the parent, with the parent having no posts assigned solely to it, then no post titles should be displayed when the parent category is selected. They should only appear on the child category, or at the end of the hierarchy tree.
For example, let's say we have a grandparent, parent, and child category named "Literature", "Books", and "Non-fiction", respectively. "Literature" and "Books" have posts under them that are also under additional child categories, and "Non-fiction" has posts solely assigned to it. When "Literature" is selected, no post titles are displayed in the list, and all posts under that category and its children are displayed in the index. The same would apply for "Books". However, when "Non-fiction" is selected, all post titles are displayed in the list, as well as the posts under it displayed in the index.
I wish someone in-the-know would "fix" this plugin to do those things with the category list. Otherwise, the expandable-collapsible aspect of it works great.