Recently, I've read (and commented on) a few blog posts about the practice of burying a St Joseph's statue in your yard to aid in the sale of your home.

This practice is widespread in the US. Although it originated as a Roman Catholic tradition, it is used by many protestants today.
The practice is simple: you purchase a St Joseph's home seller kit, which has a small plastic statue, a copy of the prayer that accompanies the statue and instructions. These kits are available at any catholic bookstore (and many non-catholic christian stores) as well as online and run about $10. I spent most of my adult life in New Orleans, which is mostly Catholic, and many Realtors in that area keep a stock of them to use on every listing.
The idea is that when you and your family (and possibly your agent) join hands in prayer and pray for a peaceful transistion to a new home, the chances are that your prayers will be answered. The statue serves as a 'tool' to aid in this important prayer.
This practice is good for anyone (we need all the help we can get!) but especially great for stressed home sellers and families.
History:
>>The custom hearkens back at least to the great St. Teresa of Avila (A.D. 1515 - 1582), foundress of the Disalced Carmelite Order. As her Order spread, a new convent had to be built, and in order for a new convent to be built, land must be had. When the nuns found a particular piece of land that was perfect for their purposes, they also found that their coffers weren't full enough to purchase it, so they decided to ask the intercession of St. Joseph, burying medals imprinted with his likeness in the ground of the desired property as a sign of their prayers. It worked.
Over the years, this evolved into the practice using the statue. Estimates are that over 2 million US homes have been sold using the prayer and statue to date.
Obviously, the most important part of this tradition is the prayer. There are many versions of the prayer on the internet. A truly heartfelt prayer of any kind that asks for a peaceful transistion is the one that will bring the best results.
It is important to point out that the statue does not bring luck and by itself won't bring about any particular result. The prayer is to God, not to the statue. The statue is just a piece of plastic and the tradition of burying the statue simply aids in prayer and focues intent.
I'm always sensative to cultural and religous beliefs of my customers. If you have catholic or christian customers who are open to prayer, this cxan be a touching and helpful addition to add to the sale of your home. Staging, after all, does reduce stress and increase the likelyhood that a home will sell and this fits right in.
Happy home staging!
When clients ask about the St. Joseph's statue I tell them I can do better than that. They even have a greater chance to sell their home if they use a Realtor named Joseph. And since the Pope has just declared two of my last sales bonafide miracles, I only need one more to be a saint myself!