The AccessWorkspaceFactory is used to read personal geodatabases, which are geodatabases stored in an access mdb. The OleDBWorspaceFactory is used to connect to a database using an OLE driver, could be an Access database, could be another type of database. The OLE connection would typically be used on a database that is not a geodatabase. Since OLE connections are not necessarily connecting to Access, they have more parameters to define. Typically you would define a DNS in the dataconnection utility in the Advanced section of the control panel(XP) and reference that file to connect. In my experience I have found OLE connections difficult to work with, slow and flaky so I try to avoid them if I can. The personal geodatabase was a favoured data format prior to the file geodatabase so the AccessWorkspaceFactory was used a lot and is typically quite reliable. It works on non-geodatabase access mdbs as well. Aside from limitations of mdbs themselves, the chief complaint about the AccessWorkspace I have heard about i is that it offers too much latitude in what it will allow you to do.