A couple of years ago, the EPA instituted new lead regulations covering work in homes built prior to 1978. After years of study, it was determined that the dust created from renovation and remodeling work in homes with lead paint was the leading cause of lead poisoning in children and adults. The dust created during construction project is much more readily absorbed into the body, as opposed to large peeling paint chips, which had been thought to be the leading cause in the past.
So what is the big deal about these new regulations? The safety, training, and work environment requirements add significant, if not prohibitive cost to any work being performed in an environment that contains lead. The work area must be sealed from the rest of the house, tradesmen are requiured to wear full suits, and respirators, and the work area must be thoroughly cleaned, and wiped down daily. There are ways to mitigate these costs, but if lead is present in the home, there is really no simple or inexpensive solution to the problem.
Here are some links from the National Association of Home Builders, and the EPA with additional information: http://www.nahb.org/generic.aspx?genericContentID=118467