Does the mansion still exist?
No - an office building occupies the location now. It was called the Wilshire Phantom House, located at the north corner of Wilshire and Crenshaw. It was torn down in March of 1957.
What is the correct title - "Blvd." or "Boulevard"?
The title is shown in the
opening shot as "Sunset Blvd.", stenciled on the curb of the actual
street (in the gutter, if you want to consider the symbolism). It is
also listed as "Sunset Blvd." on its Library of Congress registration.
However, it is very common to find it listed with an unabbreviated
"Boulevard", and was named as such in its original trailer.The movie poster on this site shows "Boulevard" spelled out.
A NOTE REGARDING SPOILERS
The following FAQ entries may contain spoilers. Only the biggest ones (if any) will be covered with spoiler tags. It is assumed that no one who is diligently avoiding spoilers will be visiting this page in the first place.