Maybe someone can set me straight. On my blog template the link to “Posted in” operates in the same manner as a Tag link. Shouldn’t the “Posted in” link act like a category link? (I’m coming over from Blogger.) I’m not even sure I can fix the error if it is wrong in the HTML since I only have editing access to the stylesheets.
The tags and categories listed under your post will lead to the WordPress global tags pages where tags and categories become the same thing and both (under the post) will lead to http://wordpress.com/tag/whatever the tag or category is/ . The global tags page will have your posts as well as the posts anyone else using that particular tag or category on WordPress.com.
The tags or categories in your sidebar will lead to listings of posts on your blog that have that particular tag or category assigned to them (local).
It’s all quite confusing. The global tags/categories pages (tagegories?) pages give more search engine juice not only to WordPress, but also to the individual bloggers.