The performance of a WF application depends on many different factors, including persistence pattern, activity complexity, tracking usage, and so on.
Marc Mezquita discusses more in his GREAT article "Performance Characteristics of Windows Workflow Foundation"
My Books......
Pro .NET 1.1 Network Programming, Second edition
Pro .NET Directory Services Programming
WebSphere and .NET Coexistence
Integrating DB2 Universal Database for iSeries with Microsoft ADO .NET
DB2 UDB V8.2 on the Windows Environment