Wow! What an informative thread! I was unaware that they used "yours faithfully" in the UK, but then I don't get out much. It sounds so quaint to me.
Mr. P, I think it is in "Marjorie Morningstar" that the heroine copies out a letter she has just written to some man all over again on a fresh sheet of paper, just so she can sign it with the cool, breezy "Best," rather than whatever she had before. When I read that I'd never thought of "best" as a closing for a letter, and I'm embarrassed to admit I signed lots of letters that way for a while because I thought it seemed cool and breezy too