Situation: Gradual migrating from a custom intranet with workflows to SharePoint; determining whether SharePoint Foundation or SharePoint Server would be required to achieve the needed functionality.
Result: A smooth transition to the SharePoint intranet that did not involve sacrificing critical functionality previously provided by the purpose-built intranet. Flexibility of AD lookups, file saving, and data string extraction provided through HarePoint Workflow Extensions noted as key facilitating factors. Reduced coding and seamless linking of complex datasheets.
Bottom line: No need to purchase SharePoint Server, short-term costs minimized while still receiving long-term benefits of a SharePoint intranet.