As a one-time Cooperative Extension urban gardening agent, soil lead is indeed a problem, mostly from leaded gasoline and the leaching of lead paint. However, there are many things you can do to reduce lead contamination of vegetables. Adjusting the pH levels in the soil reduces lead take-up, increasing organic content in the soil reduces lead take-up, choosing what to grow can reduce lead ingestion - fruiting crops take up the least amount of lead, leaf crops take up the most.
The Boston area has been dealing with this issue since at least the 1970s and many community garden sites have had clean soil trucked in. Of course, testing your garden soil before planting is advised.
For more information, The Food Project (http://thefoodproject.org), a local urban gardening for youth organization, has done studies on lead soils and contamination.
