Both "they work" and "they don't work" are unsupportably broad. Google has substantially reworked their interviewing process on at least one occasion, producing a big change in results. Story here: http://www.nytimes.com/2013/06/20/business/in-head-hunting-b...

Meanwhile it's crucial and nigh-impossible to identify how much success is based on interview performance as opposed to selection effects in who interviews, and how interviewers see different candidates.