I don't usually get nostalgic, but here's a tool I use sometimes to see the way Internet sites were in the past:

Wayback Machine

You can use it to see how Google's homepage has changed since they first launched 12 years ago (not much) or how Amazon's homepage has evolved (by leaps and bounds). An interesting repository.

I think social media is lacking this in some places. I think it would be interesting to be able to see what people had posted on their Facebook pages in prior years on major holidays, like Thanksgiving or Christmas. (Would make a good addition to watching A Christmas Story on TBS 12 times in a row.)