Tags can be used to freely organize Joomla! content items (Tagged Items) in a more simple manner, you can attach multiple Tags to a single item and build a menu-like structure with the Tags using the dedicated Modules. Another module can be used to show a tag-cloud and another one can be used to show related items (items that share the same Tags).
Adding tags to item is super-simple: Ajax powered live-search alllows you to scan the existing Tags while you type and to select matching Tags from a list, to reduce the risk of typos and duplicated Tags.
PowerTags is definitely the best solution with a full component admin panel and an excellent content plugin.
The support is just perfect, fast and very efficient, ready to upgrade PowerTags to help you.
Thanks a lot !