I assumed that there would be server side API to open an Excel document from a document library, do some processing and commit that file back to a library.
I know that there are Excel Web Services, but not really what I need (plus thats an Enterprise only feature, we are Standard here).
For example, something like this? http://blogs.msdn.com/b/ericwhite/archive/2010/03/24/modifying-an-open-xml-document-in-a-sharepoint-document-library.aspx