The 1940 census was released by the US government back in April I believe. Since the release you could view the data through the government website. However it is not searchable by name. You have to know the enumeration district and street the people you were looking for lived on in 1940. Not too helpful since I would think most researchers use the census to discover where their family lived, few us know what street (sometimes not even city or state!) that our people lived on in 1940.
Ancestry.com has been busy indexing the 1940 data since the release and have just recently completed all states and territories. The best part is they have made the data free--you do not need a paid subscription to find your family in 1940. However you do need to registrar for their free account.
I have found numerous ancestors in 1940 and while I have not crashed through any major brick walls I have answered small questions and discovered interesting facts, as well as finding new mysteries to solve. What I like best about 1940 is the question on place of residence in 1935. Those 10 year stretches between census years can leave gaping holes, a lot can happen in 10 years. If you are lucky maybe one of your ancestors was chosen to answer the detailed questions on employment. They included these questions for about 5% of the population.
You can view (and print) a blank 1940 census form with all the questions at Ancestry.com at:
1940 Blank Census Form
To search for your ancestors at Ancestry.com:
1940 Census Data