We have recently moved our SEO text from above the fold/products to below the fold/products and haven't noticed any changes in organic results. The reason for this is because the SEO text was pushing all the products below the fold and we noticed a significant jump in conversion rates once we changed the way our category pages were set out.
We generally try to go for 2-3 solid paragraphs of SEO text that explain the features, uses, brands etc of a certain type of product. Of course, this isn't good for just SEO, but it gives a basic overview of the product type to the customer.
We've also added a basic SEO tag at the top of each category, just under our logo so that our keywords are closer to the start of the code.
I'm not sure of the rules of posting your own URL, so apologise if I have broken any rules, but here is an example: http://www.kitchenwaredirect.com.au/Appliances/Soup-Baby-Food-Maker