I know this is an old thread but I thought I'd put in my experience for anyone that will be looking for this information later.
I bought the acrylic lenses off of ebay. I have put nearly 12,000 miles on the car since I replaced the lenses. The lenses have not done what most people would expect. They have not pitted or hazed. The problem with them is that they are now concave in the center instead of the normal convex shape. I'm thinking that this is due to the heat of the bulbs or possibly from the extreme highway speeds I often drive
FYI, I am not using any off the wall, high wattage bulbs. Just the standard Sylvannia bulbs.