I suggest we introduce tags clearly showing that a document class is concerned.
book-class would be clearer than just book and would not interfere with questions regarding books - those made of paper.
letter-class could be distinguished from questions regarding letters as such.
slides-class shows that the class is meant and not the concept slides including beamer.
A first glance at the tag shows that a class is meant. We could omit a documentclass tag usually.
If I would get some positive comments and the question, let's say, 10 upvotes, I would create the [tag:*-class] tags plus some synonyms. For instance, beamer would be a good synonym for beamer-class but slides perhaps not for slides-class.
memoir-classandkoma-script-class? Because that could be confusing – Seamus Mar 22 '11 at 18:21koma-scriptis not a class. If at all, thenscrbook-class. However, most non-standard classes have unambiguous names. Also, we now use plural tags, classes have singular names. I'm not satisfied withbookfor the book class andletterfor the letter class, but for now I don't see an urgent need for action. – Stefan Kottwitz♦ Mar 22 '11 at 18:33