Loosen a zipper. If your zipper is giving you trouble, rub a bar of soap along the teeth to loosen it up.
Keep fingernails clean. There's nothing worse than the feeling of dirt under your fingernails. Before you get your hands dirty, rub your nails into a bar of soap to stop dirt piling up under your nails.
Sewing a hem. While chalk is often used to mark a hemline, a bar of soap will not only have the same effect - it will wash off more easily.
DIY pincushion. Wrap a bar of soap with fabric and use a pincushion.
Remove shoe odour. Place a bar of soap in stinky shoes overnight to remove bad smells.
Pest repellent for plants. Mix shavings from a bar of soap in a spray bottle and spray on the underside of plant leaves.
Wallpaper removal. Removing wallpaper can be tricky. Make up a solution of soap and water to spray on the wall before removing.