Tiering, however, poses some drawbacks for marketers. For one thing, most programs fail to measure the potential value of a customer. Most companies can still measure only past transactions--and some find it tough to combine information from different business units. The problem, of course, is that what someone spends today is not always a good predictor of what they'll spend tomorrow. Life situations and spending habits can change. In some cases, low activity may be a direct result of the consumer's dissatisfaction with current offerings. ''We have to be careful not to make judgments based on a person's interaction with us,'' cautions Steven P. Young, vice-president for worldwide customer care at Compaq Computer Corp.'s consumer-products group. ''It may not reflect their intentions or future behavior.''