[quote user="Rob Golding"]Once the Value for the tags are set, they should not change until removed from the design.[/quote]
Unfortunately this is the only thing that cannot be asured and the reason why many programmers do not use tags, if consistency is required.
While the idea of using tags for displayable informations is a good one, you must be aware that each information might be manipulated by the user. Even parts, or the whole tag can be deleted by mistake, so you need a little goodwill. On the other hand, while there are other solutions for storing additional data, it is more difficult to get those data displayed, so if you trust your users that far, tags will be fine.