It seems there is some cleanup that should happen after sweethome3d is closed. For example I am on a Vista system and every time I start sweethome3d (and that is about 10 times a day) a new directory is created in C:\Users\???\AppData\Roaming\eTeks\Sweet Home 3D\work\some directory\ which always has the same files in it. If sweethome generates this every time it should remove it every time. I did not know about this directory and when I checked the size on the disk it was more than 20GB of information that is not needed.