I read to DD from her being about a month old. Just showing her pictures in baby soft books and talking about the pictures. I know she isn't old enough at that age to understand, but it was something for me (and DH) to talk to her about - rather than just baby sounds and coos, etc. She has had books around from birth, and we started making her a photo album straight away with familiy people. M&S do a lovely soft baby album. As she got older she loved the touch and feel books, and the ones with moving pictures and shiny pages, and lift the flap type books.
DD adores books. She is now 2y 5m and she has hundreds of books and we read them at all times of the day, with a bedtime story everynight. She's had a bedtime story properly since going into her bed at 18 months and we read a whole range of books: Gruffalo, fairy stories, Alfie and Annie Rose, Dr Seuss, Little Miss, etc.
Books are a major part in our day to day life, but they always have been. My parents were the same with me, and my sister in particular is a huge reader.
I don't think it is ever too early to start at all. It doesn't matter if they don't listen to the whole story, or even if you just talk about the pictures ont he page. Lots of interaction, asking questions, pointing, etc. And above anything else, it is quiet time together...and that is just as beneficial as the reading and listening aspect, if not more IMO.