On the Web, this is not as simple as just tossing up a variety of ad executions and counting the clicks for the differing promotional offers.
Indeed, studies have shown that extrinsic rewards, such as promotional offers, can erode the intrinsic motivation underlying consumer intent. Here's the top-line on one recent study.
So the risk is that by "buying consumer interest" as demonstrated by a click-through response to a sales promotion offer, marketers may actually demean the value of the brand in the eyes of consumers. It is vital that the entirety of consumer brand response be modeled and measured, and not just the click-through rates.
Advertising should always have a well-conceived communication strategy that is based on a leverageable consumer insight. It also helps to have a Big Idea based on the strategy.
Of course direct response methods are critical to success, but scattered testing of discount offers to promote click-through rates can erode the brand's vital value proposition.
Data mining should always take place in the context of smart strategic thinking. Said another way, you don't have a science unless you are testing a theory. Here's a link to more on the study shown in the chart.