I've found it's best not to use tags, and instead interlink your posts a lot within your content aka Wikipedia style.
Picture it like this, you have a blog with 5 pages and have a PR5 backlink. The authority from that link is is split between those 5 pages giving them a certain amount of authority each.
If you add 5 tags to each page, you will now have 5 pages of content and 25 pages of tags making it 30 pages total. The authority from that PR5 backlink is now spread between 30 pages.
You don't really want that, you want all the authority consolidated to where it counts and that's your strong content pages that will pull visitors and convert.