Honestly I only purchased this book for the novella Alpha & Omega to read the beginning of the Charles & Anna relationship. I think it's good to read this story first, yet it's by no means required. But it gives you more in depth detail to to their relationship to see where it began. Maybe someday I will take a stab at the other authors in the Anthology, but for now I'm happy with just Patricia Briggs'. 
 February 2012: Just finished "Inhuman" by Eileen Wilks. Since I've been reading the World of Lupi series. It was a nice novella set in the same world as the series, but not with any of the characters we already know. It takes place about a month after the events of Blood Lines. Kai and Nathan are both not entirely human and I liked their story a lot. I think Kai and Nathan will both make cameos in Night Shift (book 4 in the series). I don't think it's essential to read this story in order to understand the series, but just kind of enhances the world a little bit.