Problems on a whiteboard don't test programming skills simply because the whiteboard isn't executable. You don't get the feedback that REPL gives you, so you can't build up your solution - and understanding of the problem - iteratively.

Seems to me that holding a code retreat and pairing with interviewee's would be more realistic. It would eliminate at least some of the pointless stress of interviewing and would get closer to a real programming environment.

It's not like nobody has enough computers so you have to use whiteboards.