Charles Torre has posted up a very good Channel 9 video explaining InfoCard:

"Ever wonder what InfoCard is all about? Well, Nigel Watling, an InfoCard Technical Evangelist, and Andy Harjanto, an InfoCard Program Manager,  sure can explain it all to you. Here, they discuss all aspects of InfoCard (with a lot of time spent on the whiteboard). We're joined by a special guest towards the end of the discussion, who you'll see more of as we cover InfoCard architecture and internals in an upcoming Going Deep episode."