I recently read an article on Biz Reports that quoted a survey by Razorfish. Razorfish surveyed 1,000 "connected consumers" those that use social media tools like Facebook and Twitter. They found that 44% of Twitter users and 33% of Facebook users use those mediums to keep up to date with promotions and discounts from select marketers.
The article goes on to talk some mumbo gumbo ad speak that makes all big agencies feel good, but I like to put things in laymens terms for the "common joe" to understand, so here goes. Big advertisers like Starbucks, Dell and Whole Foods have found a cheap (can you say FREE) way to keep people engaged with their brand. A cheap way (FREE) to distribute coupons and special offers. Better yet, they are distributing these to "connected" people. People who will tell other people how great they are.
If Social Media does become one big coupon book, watch out Newspaper, Magazine, Radio, TV and Direct Mail (to name a few). The old school push model of coupon distribution may just go the way of the VCR.