A recent case study on ibm.com just crossed my desk...
The environment is so valuable that today DaimlerChrysler deploys 40,000 Lotus Notes and Domino applications spread over nearly every aspect of its operations. These range from standardized applications such as group discussion databases and document libraries to custom-developed applications covering complex business processes such as change management, quality control and technical specifications.40,000 users -- 40,000 applications. The ROI of being able to deploy one product to tackle messaging, sharing, and workflow is clearly how DaimlerChrysler benefits from Notes/Domino today.
For competitive reasons, DaimlerChrysler generally refrains from discussing specific processes and return on investment figures, but executives report that many of the applications are "intensively used and a huge success."
Link: ibm.com: A standardized, global system for communication and collaboration helps DaimlerChrysler compete >