I don't think most people one-box. Maybe most LW readers one-box.

I have two real boxes, labelled with Newcomb's problem and using 1 and 4 quarters in place of the $10k and $1M. I have shown them to people at Less Wrong meetups, and also to various friends of mine, a total of about 20 people.

Almost everyone I've tried it on has one-boxed. Even though I left out the part in the description about being a really accurate predictor, and pre-seeded the boxes before I even knew who would be the one choosing. Maybe it would be different with $10k instead of $0.25. Maybe my friends are unusual and a different demographic would two-box. Maybe it's due to a quirk of how I present them. But unless someone presents contrary evidence, I have to conclude that most people are one-boxers.