There used to be a Domino's case study on Microsoft's site.. they used it for routing / delivery. It's extremely varied, I've done work for people planning training classes around the country and trying to pick the optimal location to host the class. Also, I've done work for a newspaper wanting to examine distribution & delivery patterns. I've also helped a real estate company with plotting properties and a software company that integrates MapPoint for planning / tracking residential service calls. A lot of people use it for managing fleets of vehicles though there are now some EULA restrictions regarding that. See the Gallery section on this site and also I noticed some good examples on Winwaed.com the other day.
You might also take a browse through the
MapPoint Partners site, that will give you more examples.
HTH,
Eric