The Nielsen Norman Group (NNG) publishes a variety of research reports on Intranet design and usability. They are the gold standard for info and stats on intranet design and user behavior.
Each year NNG analyzes hundreds of intranets and judges the best of the year. They publish a design annual that highlights the 10-best.
Throughout the year they publish a lot of good information, and regularly update a 9-report series on Intranet strategy.
The Straighten The Maze approach has been developed in-part, by using NNG research. It has been foundational knowledge that I’ve mashed-up with the way SharePoint is intended to work, and the practicalities of managing a business.
NNG is a great source for statistics and thought-provoking information.