I've spent a bunch of time on the phones the past couple weeks calling into online retailers and asking them about their segmentation techniques when developing marketing campaigns. Typically, marketers are expressing to me the desire to segment based on a customer's purchase history using RFM data (recency, frequency, monetary). This is an excellent starting point, but it might overlook an incredibly important group: brand ambassadors.
Imagine a person that follows your brand on Twitter and regularly retweets your products, is a Facebook fan and regularly "Likes" items on your site, consistently opens your email marketing messages, but doesn't spend that much money. This person loves everything you do, but you blow them off like Mean Girls do. Why no love?
If you're not doing any targeting right now, customer purchase data is a great place to start. It's easy to analyze, easy to locate and easy to write content for, but don't forget the little man. There is a good chance that you have many fans of your brand that convince their friends to spend lots of money with you (even if they personally don't), and those ambassadors should be valued and rewarded just like big spenders are.