Like Microsoft Word, PowerPoint has made a significant investment in document co-authoring for the Office 2010 release. What is co-authoring? This is the capability for multiple users to open the same presentation file and to simultaneously edit and save changes to that file. Co-authoring solves a lot of problems with the current models of collaboration, where multiple versions of files are stored at multiple locations, not to mention the proliferation of presentations circulating via e-mail amongst multiple contributors. Now, one version of the file can exist in a shared network location, and users can edit, save, print and present from that one location.
Full Article: PowerPoint blog