It depends on the product. For an e-shop with lots of products then its not length that matters but giving the person as much relevant information as possible about a product in a quick to use way. I like detailed tables so I know just what I am getting without reading loads of text. Just check out comet:
http://www.comet.co.uk/comet/html/cache/320_220884.html
However for 1 product websites then you need titled paragraphs and/or bullet points eg:
http://www.mozilla.org/products/firefox/ or
http://www.basecamphq.com/