What is tags now - This is additional attribute only.
Users can not select all documents by one Tag.
Why.
WO has one principle of grouping - I is Tree.
I think WO must has additional principle of grouping - by Tags.
f.ex. see CyberArticle.
User can see documents in tree-structure. Every document can have until 5 Tags ('Labels' in CyberArticle dictionary)
and
User can see documents selected by any Tags ('Labels' in CyberArticle dictionary)
http://www.bild.me/bild.php?file=63390632011-01-14_211128.png
This feature will be very very usefull. f.ex. Tag is personage. User can select all documents by this personage.