Judging by last year's SketchUp Pro sales numbers, it's pretty clear that interior design is one of our fastest-growing markets. It's about time, too—between the piles of content on the 3D Warehouse, the availability of awesome photo-rendering plugins, LayOut and SketchUp's all-around awesomeness, there's plenty for interior designers to love.
And now there are books, too! Adriana Granados is an architect and interior designer who happens to know an awful lot about SketchUp. She's written a series of mercifully short, to-the-point manuals collectively titled Google SketchUp for Interior Design & Space Planning that are available for sale online. The books are printed in full color and I think they're really helpful.