[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.