I had a great ride this weekend, 250 miles round trip on my 750 K8.
Coming home was toward the west, into the setting sun in a clear sky. I was wearing sunglasses of course, but as the sun got closer to the horizon, it was progressively harder to see. I would have to say that I was getting blinded. I stopped for a coffee for the last 1/2 hour of sunset to let my eyes recover for the last hour of the trip which was largely in darkness.
I suppose there is no "solution" to riding into the sun but to wait it out.
Last night I watched a video of an X2 spy plane flight and noticed that the pilots had flip down visors on the outside of their helmets for the same problem. I wondered if visors like this were available for bikers?
The video is worth watching anyway.
http://www.wimp.com/breathtakingfootage/