I feel like this should be extremely obvious, but after staring at this document from Microsoft and Googling for a while I'm still at a loss as to the advantages of SharePoint Server 2010 and SharePoint Enterprise 2010 over SharePoint Foundation 2010. My users currently use SharePoint Foundation 2010 to collaborate on a handful of excel documents within the office. There is talk of expanding to have a second and third SharePoint server at another plant and at our corporate offices. If there is a reason to upgrade now would be a good time to ask for the money while we're talking expansion. Is it worth it from either an administrative or an end-user perspective? Or is the free version really just that wonderful?