It's not polycarbonate, it's the soft touch coating HTC puts on the phone.
Some careful, gentle cleaning with a soft cloth moistened with a weak solution of soap and water should take care of it.
That was my concern when reading that it had a soft-touch coating. I ended up ordering a black one with the idea of getting original cases in other colors. I have one in Cali Blue from HTC and it looks great and it's wonderfully fitted to the phone. Hopefully they will make other colors available soon.
Post pics and let us how the cleaning went.