realmaverick - 12:48 pm on Mar 9, 2012 (gmt 0)
I don't recommend you do this. I think it's unlikely that your product pages are causing a problem. Unless there is something specific about them, that Google doesn't like.
If your website is anything like mine, despite category pages individually receiving most traffic, the product pages traffic, when added up together, far exceeds the category pages.
I agree we should noindex junk, but your product pages are not junk, they're a big part of your website and they are ultimately, the thing your visitors are looking for.
Have you suffered a loss in traffic, which leads you to believe these pages my be an issue?
Ensure your product pages titles, are structured differently to the category pages, to ensure that a product page, won't be fighting for traffic against a category page.