it is not a dream any more, check this out http://www.lytro.com/
i don’t see the picture quality are any good, however it can let you pick the focus point after you took the shot, it is just like a dream for most average people. Even for myself who has reasonably good equipments (obviously no professional skills), sometime I struggle to lock the focus point (I usually blame on the lens, so I have excuse to buy new lens).
so for few hundred dollar, you can now get a camera that does the trick for you, no… I should say it lets you do the trick later~~
note that this is very good when taking portrait shots, i couldn’t see any landscape shots that were created by this camera. so to buy it or not buy it, it’s all up to you now.