Wow. I've been lurking on this message board for several weeks but this is my first official post. Now while I'm a newbie to fly fishing and have nothing to add that would be helpful, I am an Optometrist and this is an area that I might be able to assist.
Polarized glasses is like a fly rod, you really get what you pay for. Quality of polarization, aberrations, UV protection, lens material, Abbe factors, weight, and light transmission are all factors that come into play.
I will like to add, that I have been really surprised what a demand this sport puts on your eyes. Between the glare on the water, the often times poor lighting, difficult contrast, and I still don't know how anyone can keep track of some of those really small dry flies. So I would think anyone that fishes regularly would really want a pair of prescription sunglasses with the best corrected visual acuity. Another distinct advantage of a prescription pair of sunglasses is the ability to add and Bifocal/Progressive to assist in tying on that next fly.
Thanks everyone, hope I was able to add something to the discussion.