This is one of the most enjoyable Mac programs I've ever purchased. I've owned both version 1 and 2. The program makes designing room layouts exceptionally easy. Click the wall tool, click 4 times (the four corners), and you have a room. Click another button and you see it in 3D. Adding doors or windows is as simple as dragging the item from a shelf and dropping it on the wall where it should be.
I've used this program for determining if new furniture would fit in my apartment or in a moving van, laying out some friends' entire house (during construction) to help them choose things like floors, cabinets, countertops, and for helping design an in-house theater room with raised seating on the second row.
I could go on and on about the great features, but here are 3 examples. You have a PDF of the floor-plans to your home. Drop it into LI3D and draw your walls on top; you're done! Or you want to add your real wall decorations (paintings, photos) to your model, so you take a digital photo and import it into the program. And my favorite, you can find new objects to import in the Google 3D warehouse: plants, chairs, electronics, your car to put in the garage, and those are all free.
This program shines in how quickly you can get 80% of your modeling done. It's fast. The 20% that is slow is the fine-tuning of the details: wall color, crown molding, and baseboards, for example. But if you take the time you can create models which are surprisingly realistic, especially for an $80 program.