I'll take the top 5 metric charity bet. I bet that by May 7, 2015, Facebook will not be in the top 5 sites as ranked by Alexa.

I think it's an easy metric free of dispute. In 5 years, we may argue, "What is a social network?"

But I highly doubt facebook will be in the top 5.

I choose my high school as the recipient of your money when I win. :) I'll be back here in 5 years to see who the winner is. Adding an item to my calendar now. Will respond to this post with the identity of the recipient institution.