Just thought I would followup - I did bring the car in to a well respected independent mechanic familiar with LS's. He said the problem was the unidirectional tires - I did have them balanced - but he said to have it done again and tell them to take their time and rotate them. He claimed a non directional tire is better on the LS. At any rate, I went back to the tire store and this time insisted they try again and told them this story .... the manager did the balance himself and he said he had seen this - they managed to take all the shimmy out of the front end and it now is smooth as silk. No cost to me.