I went in March 2010; it was a wedding present from my wife and she also arranged for us to have a 1:1 guided tour, which I would highly recommend, especially as even my wife enjoyed it!!, which was a result cus a car is just a bit of metal to her, that is until the odd occassion she drives mine..... We also had a meal in the Christophorus Restaurant, although expensive it was well worth it due to the quality of the food and the views.
Whilst there I took the opportunity to visit the Porsche Centre opposite, which when I was there had some really nice stock..
Hope you have as an enjoyable time as I did.
Regards
David