OK, I ride in a variety of conditions, and it would be nice not to have to actually swap lenses to get the right amount of tint. For example, riding in the woods (yeah, I know. The Dark Side - mtb). There are times I'm in direct sun and others when it's dense forest and pretty dark. My eyes are kind of sensitive to bright light, so I defer to dark lenses, but it'd be nice to be able to see better in dim light. Also I like the wraparound style of shield lens, but it'd be more important to me to have the variable tint. Now, maybe they don't work too well, since if you're outside during the day, there's enough UV to keep them dark no matter where you are. So, whaddaya think?? Thanks!

...the sun-sensing lenses do not block much, if any, harmful UV. Since the sun sensor lenses were way more expensive than the plain dark lenses I wound up with, I figured it might actually be the truth, as he was cutting the dollar value of the sale substantially.

This may not be the case, and you may not care that much about the UV protection, but it was enough to stop me from getting them.

I don't find swapping lenses to be all that much hassle, and I'm using a prescription adaptor with mine, even.

I've got some sunglasses with Transition lens. I bought mine from SportRx.com. According to them the Transition lens provide UV protection.

I live in a sunny area that doesn't have shady forested areas. So I'm not sure whether they would change fast enough to be usable under those conditions.

specialized's entire line of sunglasses revolves around color changing lenses. check it out

http://www.specialized.com/bc/SBCEqSection.jsp?minisite=10080&sid=05EquipOptics

By law all sunglasses have to block UV rays. Rudy Project has some new lenses coming out with NXT technology that are also available in chromatic versions adn they change color almost instantly.