Job performance and personality (as measured in the five-factor model) are related. It appears that the relation between job performance and the five factors is more a consequence of the social aspects of the workplace than of ability. Research indicates that cognitive ability is more strongly correlated with task performance than any of the five factors are correlated with task performance. The five factors are strongly correlated with cooperating with others and enjoying the overall workplace experience, which are key components of long-term job success. Being absent from work or working as a team are correlates of personality that directly affect whether one will succeed in the workplace, and they are strongly correlated with the Big Five and not with cognitive ability.
It is worth noting that the majority of research has been on sales or other occupations in which interacting with people is required. Is it possible that these studies are skewed? Perhaps researching individuals in jobs that require very little human interaction (such as authors of fiction, like Steven King) would yield different results.
Conscientiousness and extraversion are the two aspects of the five-factor model that are always correlated with positive job performance, although conscientiousness is more positively correlated (extraversion is negatively correlated with job performance in that it appears to inspire more absence, but only when combined with low levels of conscientiousness). Agreeableness is negatively correlated with job performance within a leadership role. Openness to experience, in general, is unrelated. Neuroticism is negatively correlated with job performance.
Cognitive ability may allow an employee to complete a specific task, but the ability to work with others and to stay motivated are aspects of personality. The five-factor model is a valid predictor of workplace performance. Personality is an indispensable consideration for employers looking for quality employees.