An important thing to consider when purchasing dark glasses is whether or not people will be able to see your eyes.
Just because you're wearing dark glasses doesn't mean you can stare freely! I cannot emphasize this enough.
It took a few days of dirty looks and embarassment for me to realize that, indeed, people could see right through my shiny new glasses to my sleazy, peering eyes.
I can, uh, no longer ride the West Coast Express.