I've never been asked to something like that for a company in my region (northeast), but from what I've read in the many interviewing threads on HN, this is not

I've never been asked to something like that for a company in my region (northeast), but from what I've read in the many interviewing threads on HN, this is not uncommon in Silicon Valley. Braintree just had a front page post about their interview process here last week and it said they also have a several hour coding task which they review with the applicant in the next interview.