Development of measures to preserve cognitive function or even reverse cognitive decline in the ever-growing elderly population is the focus of many research and commercial efforts. One such measure gaining in popularity is the development of computer-based interventions that "exercise" cognitive functions. Computer-based cognitive training has the potential to be specific and flexible, accommodates feedback, and is highly accessible. As in most budding fields, there are still considerable inconsistencies across methodologies and results, as well as a lack of consensus on a comprehensive assessment protocol. We propose that the success of training-based therapeutics will rely on targeting specific cognitive functions, informed by comprehensive and sensitive batteries that can provide a "fingerprint" of an individual's abilities. Instead of expecting a panacea from training regimens, focused and personalized training interventions that accommodate individual differences should be developed to redress specific patterns of deficits in cognitive rehabilitation, both in healthy aging and in disease.