I love and use osCommerce. There is great support for it in the community. IMHO, oscommerce is only good for the e-commerce aspect and wouldn't really serve well for the "community/social marketing" aspect of the site.

I would recommend getting Joomla with the VirtueMart (http://virtuemart.net/) module. VirtueMart provides a very good shopping cart solution and you can use the Joomla CMS for all other aspects of your site.