The company I work for now relies on code samples. Then the interview tests you on the sample to ensure you wrote it. The rest is purely about your personality. Seems to work well.
A couple years back, I made a great hire. He came in for the interview, and fumbled through our generic tests (program fibonacci in the language of your choice, etc). So we said "no thanks." He emailed us back and wanted another interview, said he was on a borrowed computer, bad day, etc.
So we asked him to send us a code sample. Next morning, we get a machine vision algorithm coded in impeccable C++. I read through the ~300 lines and understood it easily on the first pass. So we brought him back, asked him to explain it, and hired him immediately.
When designing interviews, you have the choice of seeing the interviewee at his best, and encouraging him to live up to it in the job, or seeing the interviewee at his worst, and knowing that you at least made a safe choice.
