I've read the AMS review, between 7er, S-Class, A8 and LS460.
They gave the cars to German, American, Chinese and Japanese chauffeurs.

All of them despised the iDrive. The jap and Chinese prefered the touchscreen, the Americans and especially the germans the knob. The MMI and Comand were said quite similar and easy to use.

In terms of test, the times needed to do something were similar in the three (the Beemer much longer).

At the first attempt, users were quicker with the Lexus. At the second and after, all were noticeably quicker with the knobs (bar iDrive), with less failures and errors. Easier to get used to the logical menu structures, whereas the myriad of buttons in the Lexus lead to errors.

The Chinese and Japanese were happy the Lexus forbids use in motion, they founded to be very distracted by the screens while driving. The germans and americans said no to be really distracted and so preferred to have access to the system while driving.

So, the result of the test was that no system is superior to the other, but that it mostly depends of the culture, Asians preferred touchscreen and ams/europeans the knob. Especially the Germans said they did not like the touchscreen at all, and the fact that sometimes yiu use buttons on the touchscreen and sometimes real buttons.