If you haven't had a chance to read the special section on Knowledge and the Organization in the January 21st, 2006 edition of The Economist magazine, run out and buy a copy. The insightful articles in the section discuss how organizations in the 21st century need to be structured and how there are no real tools for measuring employee productivity of knowledge workers.
The articles especially "Thinking for a Living" titled after a book by the same name, also discuss the relative importance of email, voicemail, mobile phones, intranets, text messaging, corporate websites, information portals and corporate extranets.
To quote from the article, "There are three broad approaches to knowledge management. One is to create a system where all information goes to everybody, which is hugely inefficient; the second tells people what others think they need to know, which may not match their real needs; and the third enables them to find for themselves whatever they want to know. Companies like to say that their aim is for the third approach, but they do not always find it easy."
Probably though, one of the most interesting quotes is from Yves Morieux a consultant at BCG who simply says, "The most valuable human mechanisms are not measurable." He goes on to say that companies should concentrate on designing the processes that knowledge workers carry out, rather than measuring their performance. No wonder it is difficult to measure ROI.