I wouldn't really say nightmare per se, although it probably felt like that at the time. She just wasn't very practiced at estimating and making reasonable assumptions.

Back when I was in my final year of uni I interviewed for a set of blue-chip graduate recruiters who threw similar questions at me. I distinctly remember sitting in a Data Connection office somewhere trying to work out how many petrol stations were in the UK. I was terrible. But there are ways to get better at this and it's really no secret that Google asks these kinds of questions. I think they reveal two things about the candidate - how good they are instinctively, and how well they prepare.

Obviously Google asks candidates who get past a certain point to sign a NDA, but there's still a surprising amount of information out there. I was recently helping a friend (and have previously helped an ex) with interviews and preparing for the logic and theoretical comp.sci. parts was actually quite a lot of fun. Maybe because I didn't have the pressure!