This is really interesting. At first, I couldn't figure out your design from all the parts you are cutting, but then looking at
this image on Flickr, I get what you are going for.
I'm curious though, why do you have the long cross support board in the center of the bed frame, but you are using just the corners for support at the head and the foot? Why didn't you use a long wide board to support the mattress and frame at the head and foot as well? (See my sloppy alteration of your plan below.) Is it simply to save materials and to give you the opportunity to play around with half lap joints, or am I missing something?
This isn't a criticism at all, the design is a cool one. I like the look of the bed. This is a good thread and I'm glad to see it revived.