But they showed footage "through the eyes of the wearer" and they let press have a hands on demonstration, so it's not like they can really fake anything.

I did see a tiny bit of judder in the footage that was supposed to be exactly what the person wearing the glasses would see, but it was hard to tell.

In the video I saw at the conference presentation, the "holograms" were always in front of the person's appendages, obscuring things: https://www.youtube.com/watch?v=b6sL_5Wgvrg&spfreload=10

Peter Bright said it didn't suffer from that - see the Minecraft section of his review: http://arstechnica.com/gadgets/2015/01/hands-on-with-hololen...