At the top of the Historical tab, there is a dropdown that lets you pick books based on your attributes. Any attributes you add will be available in this dropdown, so that you can filter your reports to only include books that have certain attributes.
The second place you'll find your custom attributes is above the pie chart and the details table. Instead of having one table row for each book, what about having one for each series you've published? How about having a pie chart where each slice represents one subgenre? If you run a publishing company, how about one table row for each author you work with?