I just found this synopsis of a study by Computer Economics of the increasing maturity of IT Asset Management.  The main report is only free to subscribers of the site, but the synopsis on its own contains useful comments on the scope and economic justifications for adopting IT Asset Management.

About the Author

Colin Bartram's background in IT Asset and Service Management runs uninterrupted from the 1980s, and includes specifying, writing, selling and supporting software solutions. Today he contributes to product strategy and marketing for the Vector Networks group of companies. His spare time is focussed on his horse and the related demands of maintaining 5 acres of ancient pasture in Derbyshire in the UK.