Dear Anonymous,
Our experiences are like Mr. Clarke's. But, to your question, "is there an add on to interface the two systems?" I seem to remember from a Planview seminar that the answer is yes and it's called Microsoft Project Connector. This tool provides seamless data transfer between Planview and MS Project. Users can import, or check-in, MS Project schedules and resource assignments directly into Planview. And, once this data has been modified, users can then check-out the data for use in Microsoft Project. But please confirm this with Planview.
Cheers!
Mark Perry
VP of Customer Care
BOT International