You can see the article here. These mainly add to the eastern half of the country so a nice compliment to FamilySearch.
The point is, make sure you are checking multiple sites if you need to search the 1940 census. If you don't have an address for the person or family you want to find you are probably waiting eagerly for search capability. Although browsing the 1940 census for a large area like a county is much harder than in older census records (due to the larger population), the search is much better. Not only are the records clearer since they were microfilmed closer to their creation, the handwriting more like our modern handwriting, but the indexing is better quality than much of the earlier (online) indexing.
I had the opportunity to search for two families in New York state, only knowing the city, first name and characteristics and found both on the first try. For one, a family group, the search was without a surname as it was unsure. The other was for an individual in "New York City," not very specific. Although waiting for the indexes may seem slow, considering how much better the 1940 indexes are, including much more than just name and birth info, it's really quite quick. It's been just less than three months and most of the country is searchable, if you use all the sites available to you.