Return channel targeting and its simplicity are two very important aspects of what makes good advertising. These are steps that are outside the realm of the ad itself but are what is going to get you the sales you want. Making the customers job easy is what will make them want to buy your products or services.
Social media seems to have the upper hand when it comes to return channels. Being on the internet it can take all of 2-3 minutes for someone to find your promotion, click the link, and buy. This is what makes social media a great tool that has revolutionized the consumer market. When you post a targeted promotion on a discussion group or other social network you can then set a highly targeted landing page right to what you are promoting.
Radio on the other hand has a few minor setbacks. Since the majority of radio advertisements are heard in the car there is no way for an instant response like with social media. After your audience hears the promotion they can either call in, which is not as common today depending on the business, or wait until they can get to a computer. This elapsed time can cause your audience to forget, rendering your ad ineffective. Say your audience does remember and makes it home to their laptop ready to check out your site, unlike a highly targeted social media landing page you will more than likely need to set a more generic landing page seeing as you would have had a widely targeted promotion on the radio considering the size of the audience. This just adds another hitch to the long sales process.