I have co-led the development team responsible for the writing of the first edition of PMI's "The Standard for Portfolio Management", first published in 2006. Its second edition was published in December 2008. The standard, as most standards on processes, explains how the process works (or should work). It does not explain how to put it together and implement it. So you have to look somewhere else for that.
Part of my work involves coaching organisations in implementing and improving their portfolio management processes. I religiously buy and read most of what is published on the subject in English or French. More than often, I had to conclude that the book or article I just read, I could have written myself... and done only a half-job doing so. Most of the literature on the subject I have seen up to now, talked a lot about mathematical scoring models, tools and techniques, addressing mostly the mechanics of the process. It never addressed the soul of the process, the humans, and how to deal with the main challenge of portfolio management in this area, namely: "How do we get a whole organisation to live a common vision and be truly aligned and willing to make it happen through project work". Most of the books, that have been published, focus on best practices and techniques and do not discuss behavioural aspects as a key issue.....up to now!
I have talked a lot about Agile/Lean project management in this blog, often explaining that it was addressing human aspects of project management very well. The Agile/Lean community has recently entered the portfolio management arena with two pretty good books, in that context.
The first book, published less that a year ago, is "Agile Portfolio Management" by Jochen Krebs (http://jochenkrebs.com/agileportfolio/), Microsoft Press, 2009 (ISBN-10: 0735625670). It gives a good introduction to Agile project management and then goes on to explain how portfolio management works and how to implement such a process. For me, a major contribution of this book is really how the author explains what can go wrong trying to do portfolio management using traditional project management techniques. This leads the author to redefine the three variables of the "Iron triangle" of traditional project management , Quality-Time-Cost, into a new set of three variables, Quality-Progress-Team Morale, taking into account the importance of dealing with humans, their expectations and their perceptions. Jochen Krebs goes farther than philosophising on the subject; he provides metrics and explains how to measure, monitor and act upon all three variables. The first chapter of the book is titled "Motivations", which tells of the importance the author gives the human aspects of portfolio management. Later on, he also gives a good view of the various portfolios interacting in an organisation (Project, Resource, Asset). He finishes the book explaining how you can extend the SCRUM technique from project to portfolio management.
The second book still smells of fresh ink, since it was published a few days ahead of schedule on August 19, 2009. This is "Manage Your Project Portfolio: Increase Your Capacity and Finish More Projects" by product development guru Johanna Rothman (http://jrothman.com/blog/mpd/), Pragmatic Bookshelf, 2009 (ISBN-10: 1934356298). This is Johanna's third book. Her first two, "Behind Closed Doors: Secrets of Great Management" (ISBN-10: 0976694026) and "Manage It: Your Guide to Modern, Pragmatic Project Management" (ISBN-10: 0978739248) are real gems and won prizes for their quality and usefulness. I do not hesitate to say that "Manage It" is one of the best books around for giving practical advice to project managers. Her last book, as her two others, is full of real life examples and little case studies that support the principles, concepts and techniques offered. "Manage Your Project Portfolio" is really a very complete "How-to" book on how to set up and manage your project portfolio. As Jochen Krebs' book, this book addresses human aspects very well, including a very nice chapter dedicated to collaboration work in a portfolio management context (chapter 6). The chapter on metrics and measurement is also straight to the point (Chapter 10). Johanna's top-notch practical advices and examples are found all over the place up to the last page, with a great last chapter titled "Start Somewhere...But Start", one of the best things to do when it is time to go forward with taking charge of your portfolio of projects. A very inspiring book!
I do believe these are two books that, at last, give a more complete view of what is at stake when dealing with project portfolio management and will really help organisations move forward faster with implementing and improving this key business issue of the 21st century, the Project Age.

Claude Emond is one of the founders and president of Qualiscope Enterprises, a project management consulting, coaching and training firm based in Montreal, Canada. He has degrees in chemical engineering from Canada's Royal Military College (BEng) and Montreal McGill University (MEng), a MBA from Ottawa University, workshop leadership training from Le Centre Quebecois de la PNL, and is a certified PMP. He has over 25 years experience managing major public and private projects. He teaches project risk management in the Schulich School of Business Master certificate in project management and the PMP certification revision class for PMI, Montreal He is one of the authors of the current PMI Standards for Portfolio Management. Claude can be reached at 
Almost everybody seems ignorant of some basic facts about the software we create. No matter how efficient, on time, and bug free it is, when the users of it are human, it is vital to take universal human characteristics into account.
In particular, the inconvenient truth is that humans can only pay conscious attention to one thing at a time. When we do more than one thing, all the rest must be so well learned that their operation is automatic for us.
When we walk and chew gum, one must be automatic. When folks are just learning to drive, they cannot safely also carry on a discussion about something else with their passenger. When they are dealing with their work, using a computer, their focus of attention cannot also be on the state of the computer.
This has major implications about the details of the program they are using. If it deploys a modal dialog box, for example, that is guaranteed to interrupt the user's train of thought. Further any event on the screen that is not at the user's focus of attention will often be missed entirely.
If your project goals include making the application work well for the users, that demands careful design to accommodate the facts that cognitive science has discovered about humans. The best overview of these needs I know of is "The Humane Interface" by Jef Raskin, the Macintosh guy. His brief summary of the principles and rules is available on Nitpicker.pbworks.com under the book title.