A writer should be 'invisible'.
As a reader, I don't want to know about the author unless I decide I want to know about them. I don't want to open a book and find a photograph of the author with a page about their life and achievements, although I'm okay with having that at the end of the book. I like to know about a writer, but only after I've read their work. I like to form my own opinion of a book before considering what opinion the author wants me to form. Knowing, for example, that John Cheever was an alcoholic affects the way I read his work. I don't want it to; I want to believe I can read a book and make my own unique opinion. But I don't think I can. I don't think it's possible to know about a writer and not have that affect the way you read and interpret their work. So I try to avoid knowing too much about a writer, in case it affects my enjoyment of their book. One example is Twilight, as I read it with no idea that Stephenie Meyer was a Mormon. A lot of the complaints made about her forcing Mormon values on teenage girls didn’t bother me, because I didn’t even pick up on them. I like not knowing about a writer.
Of course, as a writer, I like to think that I'm quite important in terms of what I write, so I suppose I'd have to say I'm on the fence about this one.