Good explanation. I don't know if it'd be worthwhile to track logged-out users though. Lumping it in with the same data that came from the last logged-in user

Good explanation. I don't know if it'd be worthwhile to track logged-out users though. Lumping it in with the same data that came from the last logged-in user would make the data less valuable, because there's far less of a guarantee of which user the data was collected from (imagine people using Facebook on a library computer, then logging out and 20 more people using the computer before someone else logs in). I'm sure there'd be some use for the data though, so I'm sure Facebook will gather it if they don't already have plans to. They could just earmark it with the probability that it applies to the given user. Or just lump it all together as anonymous data, I'm sure there's value in that too.