Jane Espenson has another book of essays on Firefly and Serenity and somehow it came out and I completely missed it (thanks to SF Signal for the link). This one is called Serenity Found: More Unauthorized Essays on Joss Whedon's Firefly Universe. USA Today has an excerpt of Nathan Fillion's essay "I, Malcolm".
I'll have to see if I can procure a copy from my local library. The first collection, Finding Serenity, was an interesting assortment of essays, including one from Jewel Staite (she played Kaylee).