I just got word yesterday that I'll be teaching a grad class on the same subject as my book, which has been lying dormant for at least a year now. I was planning on returning to it in the Spring in earnest, and now the course will force me to. Now if only I can hold off writing the syllabus until I'm caught up with this semester!
Also, since it will be my second grad class in my first three years at this school, I'm taking this as evidence that I did ok with the last grad class.
Anyway, any advice for teaching subjects that are this close to your research are welcome.