>>while homework problems can be better than in-person interviews, they can also be a lot worse. for one, because they are NOT time-bound.

Um, this is a good thing, not a bad thing. Research shows that stress significantly reduces cognitive ability, and time pressure definitely adds to stress - sometimes substantially. What this means is that when you ask whiteboard coding questions during the interview, you're not measuring the candidate's on-the-job ability. You're simply measuring how well they perform under severe pressure. If that's fine with you, as in it's representative of your work environment where people have to churn out code around the clock, fine. Otherwise, homework questions are much better.