I have an 05 LS430 "Sport Edition" (purchased used 2 weeks ago). I, too, noticed that the steering "pulls" a bit on different roads. The steering "seems" heavy depending on road surface (crown in the middle, tends to push the steering one way or the other). I have driven numerous cars with "High Performance" tires and this seems to be the case with all. The car I traded for the LS was an 03 Z06 Corvette with slightly larger tires than the 245/45Z18's that are on the LS, and it did the same thing. Keep in mind that the tires on your car are likely wider than what you are used to (they literally take up more space on the road surface).
For the record, I absolutely LOVE the way the car handles. The steering is responsive, not mushy or lacking at all.
Do I miss the 405hp and handling of the vette? Of course, but nothing I have driven (including mom's S-class or 745) comes close to the overall experience (handling, fit & finish, interior, driver amenities, cust. service, etc) IMO.
If Apple made a car, it would be the LS430.
Hutch