I'm trying to get to grips with the correct way of using Tags, and the way I see it is that it's like the index of a book and are mainly used for the visitor to navigate your site. So they read an article, see tags relating to that article, click a tag and see things related to what they've just read. I'm far from an expert in this field, so I'm after a bit of advice on the best practice. Do you think they make much difference in terms of ranking on the search engines? Is there a maximum number, you'd recommend using on each page/post?