I think many CEOs in the U.S. now would pay attention to any luxury car he/she drives to work.  The choice is not about the Panamera, it is about perception of extravagance in a rough economy.  If a CEO arrives in his black S class Mercedes, he/she is going to be noticed. 

But I know two CEO's of large companies here who drive what they want regardless.  One drives a Murcielago, and the other drives a Panamera Turbo.  It is all about knowing your company and its context. 

I do think though that--at least on the east coast of the U.S.--CEOs are more comfortable in black luxury sedans like Mercedes, Lexus or Cadillac.  But this is more because Porsches are more known as performance cars, not luxury cars.  More traditional CEOs want to feel pampered and luxurious, and this is not (and should not be) Porsche's brand.

But let's don't get stuck in the CEO segment.  My local dealer just sold his ninth Panamera in less than 3 months, and none has gone to a traditional CEO.  They have been bought by either long time Porsche customers, or long time sports car enthusiasts.  The most recent sale(two days ago)--a silver Turbo with ceramic brakes, Burmeister sound sytem, special expresso leather, etc., etc--went to a BMW X5M owner who just loves cars.  He traded in his new X5M after having it only nine months, and bought a car with a sticker price of over $170,000 U.S.  This is crazy money, but it is there, and if you have it, flaunt it no matter what the public thinks...