Probably a lot of historical users will never tick the box to allow their data to be transferred, and that data will fall off the web, or at best be archived. T

Probably a lot of historical users will never tick the box to allow their data to be transferred, and that data will fall off the web, or at best be archived. That would happen even if there was not a time limit for users to take action; June is likely the time limit. There has already been some work on scraping an archive of Delicious and that is going to pick up steam. On the one hand, they seem to be doing things right with giving users control over their data, and complying with their ToS. Pity this means the data that got siloed away will be lost. Even when everyone does everything right, data silos are not good in the long term.