Ancestry.com has uploaded all the 1940 Census forms! They are not indexed (which means they are not searchable by name yet) but they are working day and night to get it done. They have finished Delaware and Nevada. They are currently on District of Columbia.
If you know the street and a cross street, you can look up using the Enumeration District. Fortunately, I knew the street address where my father's family was living in 1940. I had to search through two districts. They weren't in the first (26 pages) and found them on page 20 (of 36) of the second. Sidney and Selma are at the bottom of this page, with three sons and the youngest three sons are on the next page.
It is a little hard to read, remember you can click on the picture to make it bigger.
They lived at 504 Gage Street. Sid was employed for 40 hours a week at a Rubber Company (we know it was Goodyear) in the Experimental Department. He made $2400 per year in 1939 and worked 52 weeks. Selma was not employed. They owned their home, valued at $2000. He was 42 and Selma 41. My dad, Ramon, was five at the time the census was taken.
If you want me to find any 1940 Records for you, email me with the city, state, street and cross street (you can find the cross street by looking at Google Maps) and I'll see what I can do for you.