I have two sets of these Polks - one set on the rear deck and one on the front. Rear deck ones are about 3 years or so older than the front ones. This summer I sprayed a little Windex on the rear ones, wiped them down and they look just as good as the new front ones.
Love them. Great bass and range for right around $200 bucks.
Link to Best Buy although my first set was purchased at Circuit City and the last set from Crutchfield.
Ron