In college, I won a business pitch competition with the idea of using a digital laser measure to measure the dimensions of any space, and then only show you furniture that fits within that space. It had some other aspects, but that was the gist of the idea. It looks like Ikea and others are slowly working their way towards that ease of use, but it's still a ways away.

Related concept: when I moved cross-country for grad school I found my landlord on Internet classifieds and got him to send me a floor plan of the apartment; I then measured all my furniture, used LibreOffice Draw to make circles and rectangles that I could print at the same scale (that was surprisingly time-consuming - it would be neat if someone could make that easy), then printed and cut them all out and virtually re-decorated the apartment until I found a layout I was happy with. It was a neat way to do it, but rather labour intensive.

Actually it would be useful if it included measurements of your doors so that items you aren't going to be able to get into the house unless disassembled first can also be appropriately filtered.

There's an app called CSTM that takes this concept to another level with custom built furniture. The furniture is more expensive thusly but also more unique. http://cstm.co/

Taking a pic of your room and seeing nice furniture virtually added so you can easily test different styles.

In college, my senior project involved a 3d room designer using the Kinect and a laptop. You could position virtual 3d objects (couches, lamps, etc) in the room, and move the camera around to see how the virtualized items looked.

that sounds so freaking cool :D

Somebody wrote an app for that :) http://reorganize.amberfeng.com/