All I can say is I am very happy with my Smith sunglasses (Mavericks), but I have only worn cheap ones in the past, so probably don't have much basis to say anything.
I have worn my first pair for three years now, and pretty much nonstop. I work full time as a Wildlife Biologist, spending ~9 months of the year in the field. Most of my work centers on streams, rivers, wetlands, ponds and lakes, so I wear them even when overcast for improved visibility (polarized lenses). Of course I also wear them when I packpack into the wilderness over snow, and when I am out in the bright sun of the deserts of Eastern Oregon.
They work for me, and I like their Lifetime Warrantee (have not tested it myself, but colleagues have and said they had no problems).
I am not sure about all their sunglases, but mine came with a certificate that states the lenses were ground by Zeiss, which, from what little I know about optics, isnt a company whose products deserve to be scoffed at.
Anyway, I think Smith makes a good product for the money, and they work for me and what I do.
Brome