This book won't just teach you how to write a dirty story, although Susie Bright does do an admirable job of that with plenty of exercises, tips and things to watch out for.
What pleased me most about this as a read, was the lengthy introductory section about the politics and morality of erotic writing. Ms Bright is just the woman to provide an intriguing, left-wing feminist viewpoint on the US erotica industry, and I learned a lot from this section as well as the more practical parts of the book.
Also, one of the most invaluable parts for me, that really got me thinking as to what I want out of my writing, is the part titled "Money, money, money". Ms Bright asks you to consider exactly what you want to get out of writing erotica (or indeed, any sort of writing), and what you are willing to give up to do so. Her advice about the publishing industry is also very helpful.
Highly recommended, and one of those books I know I'll come back to time and time again.