Have you ever used masking tape for its original purpose...to mask walls and molding corners when painting?

I've used it to cover the Amazon logo on a carton that I wanted to re-use to send something via UPS.  I've also used it to seal the covering around my window air-conditioners in the winter.  It doesn't leave adhesive residue like other tapes would.

Yes.  There's still traces of it on the floor to prove it.. just behind the blobs of paint.

I use it for dating food.  When I pour things like flour or sugar into a container, I write the date it was opened, and the "best by" date on masking tape and attach it to the container.  Before I put bread in the freezer, I write the date I bought it on masking tape.  This enables me to not only see how fast I use things, but to keep things rotated (use old first). 

Yes. 
We use it to make concrete molds. Dividing the sides for the fiberglass casting. 

I've used it for holding the paper on a drawing-board, but can't think of any unusual uses I've put it to.