The question is, why would you want duplicate content. If your intent is to trick the SE's then you will be caught at some time. If your intent is to run a business then your customers suffers because they find the same content running through 500 domains. IMHO having more domains names puts a lot of preasure on the owner to provide usefull and unique content. Most seem to fail at this and wonder why all their sites are not listed. I think a good test is to pretend you are a customer and you are searching for your product. If you visit the same content 500 times, it's going to tick you off. Now, if you can create enough unique content for those 500 directories(sub-domains) then you can cross link them. You need to think long term because the SE's are continuing evolving, which is great. Position your company to be there for the long term and you will do well.