One thing other posts regarding tag usage haven't touched upon as far as I know is whether we should tag books. E.G. the-art-of-war for a post like this or critique-of-pure-reason for a post which specifically refers to the book (not just references it in passing). My only concern is that some book titles might get fairly lengthy, or have dual parts/usages and be harder to figure out a common tag. That will take a bit more diligence on the part of the community to fix them. E.G. enquiry-concerning-human-understanding which is as you may know a revision of a-treatise-of-human-nature.
At this time it doesn't make that much sense to me to tag particular works, though there may be reason for exception eventually. I think it is probably most constructive just to apply an appropriate author tag, even if your question relates explicitly to one particular work. Note that there aren't even that many author tags floating around yet, so unless we think it is helpful somehow I don't see a good reason to apply tags for the particular book. (If the question does deal extensively with a particular work, its full title and author should be mentioned explicitly in the body and headline so a search or skim will turn it up.)
At any rate we could do a better job of applying the author tags where appropriate as they seem completely constructive, and also hopefully lack some of the other issues you identify with tagging works with long titles and so forth.