Kozmos will be always free for private bookmarking, and there'll be a paid account for creating public collections in the second phase. Copying the details from my another comment here;

"The second phase of Kozmos will have "public collections", for example, we will be able to create a "Best Boutique Hotels in Istanbul" collection, and this will be only available for paid users. This is Kozmos' business model but I haven't explained it in the site, because collections aren't implemented yet."