As a book publisher, this is one of my BIGGEST pet peeves. For professional documents, manuscripts, etc., please put only one space. Taking them out is the first thing we do when we get a manuscript in for publication. Check out newspapers, books, and magazines - you won't find them.
Double space is not WRONG, just not appropriate professionally in certain fields.
Taking them out is the first thing we do when we get a manuscript in for publication. Check out newspapers, books, and magazines - you won't find them. 
Hybrid Mode
