Rel8tion was developing a system for matching up a person's location and their demographic profile with relevant ad inventory, according to AllThingsD, which was able to pull a bit of information off the startup's website before it turned into the mysterious black page that it is today.

While Facebook won't officially confirm what its plans are for Rel8tion's technology, it's pretty easy to decipher: location-based advertising. On mobile. Using your Facebook profile info.

In fact, speaking at the Inside SocialApps conference yesterday, Facebook CTO Bret Taylor confirmed the company's primary focus in 2011 is mobile.