How can I make performance reviews less painful for all concerned?

There was a time when people knew each other and box-ticking exercises were not necessary, O tempora o mores! Managing relationships with colleagues and staff should be a year-round task but all-too-often problems are allowed to fester - and the ritual of an annual review will not be enough to defuse the situation, if anything it just creates more tension.
How can I make performance reviews less painful for all concerned?