When building applications to solve a specific business need, I'm a big fan of using the 2007 Office System as a base platform.  Why?  If you're building a web application, it often takes a lot of code and will still limit user functionality. If you develop a rich UX application, it will serve the user better, but it's one more application that the user has to learn and use to get their job done.

With an application built on top of the 2007 Office System, you can do things like let the user stay in their preferred application - say Microsoft Outlook, for example.  This is an example of an Office Business Application (OBA).  OBAs are an emerging class of applications that connect users to exising LOB systems through the familiar Microsoft Office interface.

For a great example, check out the OBA Reference Architecture Pack for Supply Chain.

What do you think?