One way is to make a selection of the furniture. On a new layer, fill this selection with black. Then play with the transform thingies (distort, perspective, etc) to slant the silhouette down and flatten it some so it’s consistent with the slant angle of the floor. Blur and adjust opacity as needed.
If the furniture is not already on it’s own layer, you might have to use the selection to copy and then paste it on top of the background layer; this allows you to place the shadow layer behind the couch.
The old way to do shadows (before drop shadows were added as a layer effect) was basically to do what glen said: one created a shape from the original item with pen tool, lasso, etc. One then created a new layer and filled this shape with black. Guassian blur was added. The shape was moved to offset it slightly from the original and then the layer was placed under the original. The shadow layer was generally set to multiply mode and the opacity dropped to 30-50%. Sometimes one further masked the shadow by adding a layer mask and filling with a gradient fill.
A touch of noise can be good, too.
This "old way" is still viable because, sometimes, you just can’t get the shape and size of shadow you want using the drop shadow layer effect.
=-= Harron =-=
