Possible Duplicate:
The SEO Benefit of Breaking Up Content Onto Different Websites

I was wondering if (assuming all your content is related) it would be better to put all your content under a single domain or multiple domains that link to each other. Lets say I have Site A which doesn't have a good search ranking. If I have a new product that I'm sure could get a good ranking on its own would I get a better search ranking for Site A if I -

1. Add the new product as a new section to Site A.
2. Or put the product on new Site B and link back to Site A.

To give you an example if you were developing a few browser plugins would it be better (in terms of ranking) to showcase them all in the same site, or would you give them each their own domain's that link to each other?

Thanks.