Cover Story: Top Dog

"It generated buzz within the Twitter community and among industry experts, and 40 percent of purchasers were new to PETCO."

The campaign was brilliant on several levels, according to Smith-Harmon's White. "[This] PETCO promotion rewarded sharers while also allowing PETCO to identify sharers, which could be used in segmentation later in addition to the follow-up email delivering the reward," White wrote in his blog, The Retail Email Blog, on Aug. 24. "What PETCO has created is a two-tier promotion where sharers are rewarded for driving more sales from sharees. When some retailers are troubled by promo code sharing, this provides an interesting way to deal with it — make the code less valuable but reward the sharing."