I wish schools would stop using it so much. Mercator is useful, yes. But having good size comparisons is much more important for most everyday tasks.
Is the use of Mercator in schools common, globally? Based on what I've read on the internet it's common in the US, but I have no idea about other countries. In Finland I think I only ever saw Robinson or Winkel-tripel type compromise projections. Mercator was maybe used as an example of how projections distort things.
I don't think I've ever seen a Mercator map of the world printed out, though. Is that seriously a thing? It looks completely ridiculous. Every poster I've seen has been a more rectangular projection like Robinson.
Edit: I just noticed that Google Maps on Firefox and Chrome is indeed 3D, but on Safari it is 2D Mercator.