[ajepst]

Yes, they are necessary. I've seen "senior" people bomb on it. There's a segment of "developers" that are good at selling themselves as programmers, manipulating the interviewer so you talk yourself into thinking they are awesome. You've probably met some of these types at conferences, and think they'd be a worthwhile hire. But stick a simple programming problem in front of them, and they can't back it up. if you're not that great at spotting these people, they can slip by the average interviewer without something concrete like a FizzBuzz to show they can back up their talk. And once they make it into your organization, if you don't catch them early, they can be extremely destructive.