Well, this is one entry that won't be getting a personal photo.
As is turns out, crystal frames let through sun just fine, so no temple tan lines. BUT...if your sunwear is any good, which mine always is...than the UV protection in the lenses will also provide sunscreen for the skin around your eyes. Which is totally great for the prevention of additional "smile lines" (ahem).
The end result, however, after a day of boating fun is two lens-shaped white shapes around your eyes.
So love crystal sunglasses. Just don't expect them to provide you with the perfect tan.
Also, I'd recommend staying away from the Lolita-esque heart-shaped sunnies if you're expected to appear in public after your day in the sun.