I've blogged about the book of poems vs. the project book in the past, more than once in fact. Recently I've found a site devoted to the project book, asking such questions as:
"What makes a book of poetry a project book, and what separates a successful project from an unsuccessful one? How does taking on a project affect a poet’s writing process, and what does the proliferation of project books in general signify for contemporary poetry?"
Hosted by Cynthia Marie Hoffman and Nick Lantz, The Cloudy House features interviews with poets who've explored the project book, including Caki Wilkinson, Shane McCrae, Oliver de la Paz, Julie Carr, and more.
It's a terrific resource.