From the National Archives website on the subject, the 1940 Census will be released on April 2, 2012. Digital images will be available via Internet as well as at NARA facilities nationwide.
The census day was April 1, 1940. There are many standard questions in the census but also a few new ones such as whether the person worked for the CCC, WPA; what is the respondent's usual occupation, not just what he/she is doing currently; and identification of who is supplying the information for this census entry. For a detailed list of the questions, as well as the forms, visit the NARA site listed above.What can you do now in preparation for the opening of the 1940 Census?
1. Make a list of all the people you want to look for in the 1940 census. Think broadly--ancestors, their siblings, cousins, etc.--anybody to whom you are related.
2. Collect addresses for these people for whom you plan to search.
3. Identify the enumeration district (ED) in which each address was located
(Suggestions from the NARA Start Your Research website on preparing for April 2, 2012)