I needed an application to build a portfolio with nested categories (among others for keyword galleries) and the possibility to assign a product (in this case the artworks) to more than one category. To avoid double content each artwork had to be found only under one unique url. Because I set up the whole site with Joomla I gave a trie to Virtuemart. And it does the job better than all the galleries I tested. One reason herefore is that Joomfish support work quiet fine.
So ... have a look at www.michael-quarz.com.
bye Micky