[StavrosK]

Hmm, this is similar to http://historio.us, which I built. However, this doesn't require any user interaction, which might work well.

Do you store just the URL and depend on Google returning the results? How does it work exactly?

[andy_boot]

I remember thinking that http://historio.us was a neat idea.

But Seen Before requires less effort on my part as a user -> I am more likely to use it. I just continue to google as per normal and now I have an extra option on the right to filter results.

[StavrosK]

This is true. The use cases are a bit different, but I still don't know exactly how this works so I can't say.