My favorite interview had me desperate to ask a programming question that one particular "expert" candidate could answer. After asking successively simpler questions, I ended up asking him to implement a while-loop using [drumroll] if and goto.
"Sure, that's easy!", he replied.
I offered the whiteboard marker. "Can you show me?"
"Of course!", he nodded, not moving to take the offered marker.
"Will you show me, now?"
"Sure, I could do that!" ... [pause]
"Please show me now." ... [pause]
"Well, no, I can't."
Here's the flip-side of all this, though. I love good programming interviews. Sure, there's only so much you can glean with these distilled and contrived programming problems. And yup, I've bombed some interviews that I smacked myself over later, and that I believe underestimated my true abilities. That said, answering puzzles like these for four to eight hours during a grueling day is my idea of a Good Time. Call me crazy, but isn't that why we've picked this career anyway?