I've worked in companies with both good and bad HR departments. Currently, our HR department, has intervened in our department hiring processes because they saw incredibly high - and quick - turnover in some groups. In those groups, they have improved the interview process significantly. Not by taking over, but by forcing the managers to be more honest when posting and discussing the positions, by forcing the managers to actually learn "better" interview skills and techniques, by forcing the managers to be more realistic about job requirements (do you really need someone with a Master's degree to staff your standard Tier 1 or 2 helpdesk????? OMG, NO!!!)