Should Magento have a dedicated theme specially targeted for mobile phones and tablets, or should it have one single responsive theme that works in desktop browsers as well?

In Magento one can set up multiple themes. One of these themes can be specified in the admin panel that should be picked up by Magento if a user is accessing the store from a mobile or tablet device. Of course this theme has to be a slim down version of the original website theme so that it loads faster on mobiles and tablets. Magento admin interface allows this to be done from System > Configuration > Configuration Scope > Design. Here’s a good article on how to do this.

This approach has a downside that a new separate theme has to be created specifically for mobiles and tablets.

However, what if one single theme was sufficient enough to display your online store on all platforms. I am referring to responsive design which adapts itself to the screen resolution the user is using to view the website. You can read more about responsive designs here.

This approach has its own downside that the website may / may-not load with the same speed on mobiles and tablets which have limited connectivity.

Ultimately the the choice is with the client and/or the designers. Personally I feel that Magento should have a slim down version of theme for mobiles and tablets so that page load speed can be optimized for devices running on low speed connection.