I have a large shop with over 9000 products and over 60000 product attributes. :) I'm happy to say that Easypopulate works quite well. :)
Only downside is that I can't delete attributes? If I remove some attribute from my CSV file, it's not removed in oscommerce. The solution so far has been that I have simply truncated the orders_products_attributes table, then EasyPopulate will add all new options..
But now I have added some manually maintained products which have attributes as well, so I need some more clever way to remove attributes.. Any suggestions?