I make Challah on a regular basis, all by hand. I love the feel of the wet and dry ingredients as they come together. The velvety feel of the sifted flour, the creaminess of the beaten eggs and oil. The satiny smooth texture of dough perfectly balanced in sticky to dry. And the smell... oh... the smell of the yeast gives my Shabbat kitchen just the right earthiness. And when I'm ready to punch down the dough, the first and second time... I put my ear to the huge mass and listen to Hashem's [God] creation at work as the yeast interacts with all the other ingredients as it pops and crackles.
And then... just when I think my appreciation for Hashem's creation can't get any better... I get to make a bracha! On dough! I get brownie points (pun intended) for doing something as basic as baking!
Now, with regards to the Schlissel Challah (Key Challah) it's a segulah [lit. virtue] for wealth and a happy home. often people will bake the key to their front door into the challah.
1. Based on "Pitchi Li Achoti, Ra'ayati..." ("Open up, my darling..."--Shir HaShirim 5:2), on which the Medrash states "Pitchu li petach ke-chudo shel machat...," (cf. Shi HaShirim Rabbah 5, s.v. "Kol Dodi Dofek") = something like "Open your hearts (in teshuvah) like the eye of the needle, and I (God) will open the rest like [a very large opening].
2. According to Kabbalah on Pesach the gates to heaven were open, and following Pesach the lower gates are shut, and it's up to us to open them again, therefor on the 1st Shabbat we put the key on the challah to show that through the mitzvah of Shabbat we are opening the locks [original source?].
3. In the desert the Jewish people ate from the manna until after Pesach upon entering the land (with the bringing of the Omer, see: Josh. 5:11), at which point the ate from the produce of the land, and became dependent on their livelihood for the first time (now they had no manna). The key in the challah after Pesach is a request the God should open the Sha'arei Parnasah (gates of livelihood). Alternatively, the manna began to fall in the month of Iyyar, and this Shabbat is always Shabbat Mevarchim Iyyar.
And as far as knowing if it has worked for anyone? Who knows... when I get a Bracha from Hashem, I have no way of knowing WHY I received it. I just thank Him that did.