The Murphy bed (http://en.wikipedia.org/wiki/Murphy_bed) is a traditional solution based on rotating the bed 90 degrees to form a wall, rather than sliding wood on/off it to form a floor. This guy's solution seems nicer in a way, but a bit more complex.
Actually I've wondered why Murphy beds, or something similar, aren't more common in space-constrained housing. They don't seem all that complex. The only widespread example I can think of that people actually use is Japanese sleeping on roll-up futon mattresses that can be put away during the day (though western-style beds are now common there also).
I've seen multiple apartments in old SF buildings that have a unique style of Murphy bed.
Two units next to each other will each have one room (bathroom or kitchen usually) that is elevated a few steps up.
That extra space allows for your neighbor to have a large drawer at ground level that contains his or her bed during the day. In effect, you're storing your bed under your neighbor's apartment. Unlike a vertical Murphy bed, you can use a heavy mattress and you don't have to make your bed to put it away.
It's pretty smart, but the person I knew who had one never used it because the building was old and he was convinced his bed would be full of spiders. :)
What about bedsheets, pillows etc. Also it seems it is hygienic to let the mattress air dry. I like this guy's sliding lego house: http://www.youtube.com/watch?v=juWaO5TJS00
By raising the bed a few feet off the ground you get a fair amount of storage space which is often in short supply in space constrained apartments. A friend uses 4 ropes on each side and motor / pulley system in his attic to raise the bead to the sealing which has the advantage of not requiring you to do anything to the sheets, but takes a little extra work. He even had someone paint the underside so it looks interesting up there.
And, I find people using inflatable mattresses for spillover guest bed's which take up vary little room.
They seem to be making a bit of a comeback actually particularly in spare bedroom/offices.
My mom built a "library" in their house that has one and my sister in-law recent switched the futon in their spare to a Murphy bed. I think part of it is design, newer ones are very slick.
My grandparents have a Murphy bed in their apartment. Their reason for buying it at the time was they also used the flat as a small doctor's office and the bedroom was the waiting room during day.
It has a wooden back plate on the underside so that it looks like a large black wall closet when hidden.
I think one advantage of this system over the one from the article is that it requires less vertical space.
Actually I've wondered why Murphy beds, or something similar, aren't more common in space-constrained housing. They don't seem all that complex. The only widespread example I can think of that people actually use is Japanese sleeping on roll-up futon mattresses that can be put away during the day (though western-style beds are now common there also).