I prefer just a logo. Too often the image, behind the text, makes the text too hard to read. Can't read the title...can't read the site description
I always prefer Logo rather then text over image. Blog with logo stands alone in compare to blog with text over image. DON.
Yeah I got my own header image too it's better I reckon both for "the feel of a complete site" and also like the above posts - text over images doesn't work that well