Over the year we have been rolling out the responsive layouts for our Joomla templates for Joomla 2.5 and Joomla 3.0. There is no doubt that the responsive is the way to go but it should be easier to implement. Our T3 framework helps a lot in achieving that.
Building up a responsive Joomla template for e-commerce site can be a lot of work. Choosing the right shopping cart extension again can be a hard decision. So far we have been providing support for JoomShopping and Virtuemart extension in our Joomla templates.