There is an obligation to search ones home for Hametz on the night of the 14th of Nissan, meaning, the night before the Seder. (This year, 5770/2010, Bedikat Hametz will take place on the Sunday night before Pesah.)
Generally speaking, the wife thoroughly cleans the entire house for several weeks before Pesah. Rav Yosef Shalom Elyashiv (contemporary) ruled that one does not have to search for Hametz on the night of the 14th of Nissan in the places where the wife had thoroughly cleaned. Since those areas have been cleaned and Hametz had been kept away, there is no need to search for Hametz. One must search for Hametz only in the corners, crevices and other areas where it might be difficult to clean, and there is thus a possibility that they might contain some Hametz.
There is a widespread custom to place ten pieces of bread throughout the home before Bedikat Hametz. One must ensure that he knows precisely where all the ten pieces are located, so that he can collect them all. Rav Elyashivs practice is to personally place the pieces of bread around the home, so that he will know for certain where they are all placed. He adds that the pieces of bread should be wrapped, in order to ensure that crumbs of Hametz are not scattered around the home. Preferably, the bread pieces should be wrapped in a flammable substance, such as paper, so that one can simply throw the entire wrapping into the fire the next morning, rather than using a nylon bag which one must then open to take the Hametz out for the burning.
Summary: One must perform Bedikat Hametz (the search for Hametz) on the night before Ereb Pesah. One does not have to search the areas that have been cleaned before Pesah, except the corners and crevices which may not have been easy to clean. It is customary to place ten pieces of Hametz throughout the home before the search, but one must ensure that he knows exactly where all the pieces are. The pieces should all be wrapped, preferably in paper.
