A colleague in TLC found this book, I haven't had a chance to read it yet but the abstract looks good. It's in pre-print at the moment and freely downloadable.
ePortfolio Performance Support Systems: Constructing, Presenting, and Assessing Portfolios
"ePortfolio Performance Support Systems: Constructing, Presenting, and Assessing Portfolios addresses theories and practices advanced by some of the most innovative and active proponents of ePortfolios. Editors Katherine V. Wills and Rich Rice interweave twelve essays that address the ways in which ePortfolios can facilitate sustainable and measureable writing-related student development, assessment and accountability, learning and knowledge transfer, and principles related to universal design for learning, just-in-time support, interaction design, and usability testing."