At first sight, layout seems like a useful general concept which fully deserves the 61 questions tagged with it at the moment.
On closer examination, these questions can be divided into three major and a lot of minor (tag) areas. The major concepts are:
In my opinion, "broad" concept tags are useful if there are either questions that don't fit into a specific concept or package (this is the case for e.g. diagrams) or if solutions given for a specific area are likely to be applicable more generally (this is why questions about specific list environments should also be tagged with lists). For layout, neither is the case. Every question tagged this way will need additional, more specific tags, and the answers of one layout subarea will be of little or no help in another subarea.
EDIT: "Killing" a tag (i.e., removing it from every question) can be done automatically and without flooding the start page -- Jeff Atwood did it with the picture tag.