I pre-ordered Pro OpenSolaris by Harry Foxwell and Christine Tran many moons ago and it finally arrived last week. Weighing in at just under 16 ounces, I'm looking forward to reading this one during my upcoming travels.
Unlike the much chunkier (and therefore travel restricted) OpenSolaris Bible, Pro OpenSolaris assumes you already have some knowledge of "similar operating system" features such as GNOME, networking and the shell. Therefore, if you already have experience with Unix and/or Linux, this book will cut to the chase at explaining the unique features of OpenSolaris.
I've only skimmed through the pages, but I can attest to the quality of the authors. Both Harry and Christine have years of experience working with Solaris and I've personally met Harry while visiting the Capital Region OpenSolaris User Group which he leads.
To get a feel for the book, APress has made Chapter 1 available in PDF form.