I find it hard to imagine Google being leaked

Not all their data, and not all at once, but a little here, a little there.

  The sheer amount of data

It won't be possible to collect all of Google's data. It will get easier to collect more and more of it though (as storage grows larger and the net becomes faster). I wouldn't be surprised if all the email Hotmail handled in the 90s could fit on a consumer 20TB drive from today.